U.S. patent number 6,982,515 [Application Number 10/363,243] was granted by the patent office on 2006-01-03 for dual position linear displacement micromechanism.
This patent grant is currently assigned to Brigham Young University. Invention is credited to Deanne Clements, Larry Howell, Scott Lyon, Brent Weight.
United States Patent |
6,982,515 |
Howell , et al. |
January 3, 2006 |
**Please see images for:
( Certificate of Correction ) ** |
Dual position linear displacement micromechanism
Abstract
An apparatus (1) that is capable of a first stable configuration
and a second stable configuration is disclosed. The bistable
mechanism (10) has a leg (30, 32) that is coupled on one end by a
base member (22, 24) and on the other end by a shuttle (20). The
leg (30, 32) stores potential energy as it is deflected. The
potential energy stored in the leg (30, 32) has a maximum potential
energy position with a low potential energy position on either side
of the maximum. An apparatus and method are also disclosed for a
latching mechanism (910) and the associated method. The latching
mechanism (910) is comprised of a grasping member (932), a lock
slider (928), and a detent slider (916). These three members (916,
928, 932) operate together to induce a locked configuration and an
unlocked configuration by actuating the lock slider (928) in a
single direction.
Inventors: |
Howell; Larry (Orem, UT),
Lyon; Scott (Provo, UT), Weight; Brent (Springville,
UT), Clements; Deanne (Lafayette, IN) |
Assignee: |
Brigham Young University
(Provo, UT)
|
Family
ID: |
34392846 |
Appl.
No.: |
10/363,243 |
Filed: |
September 12, 2001 |
PCT
Filed: |
September 12, 2001 |
PCT No.: |
PCT/US01/28614 |
371(c)(1),(2),(4) Date: |
March 05, 2003 |
PCT
Pub. No.: |
WO02/23606 |
PCT
Pub. Date: |
March 21, 2002 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20050073380 A1 |
Apr 7, 2005 |
|
Current U.S.
Class: |
310/307 |
Current CPC
Class: |
B81B
3/0054 (20130101); B81B 3/0062 (20130101); H01H
1/0036 (20130101); H01H 61/04 (20130101); B81B
2201/037 (20130101); B81B 2203/051 (20130101); B81B
2203/053 (20130101); H01F 2007/068 (20130101); H01H
2001/0042 (20130101); H01H 2001/0047 (20130101); H01H
2001/0078 (20130101); H01H 2061/006 (20130101) |
Current International
Class: |
H02N
10/00 (20060101) |
Field of
Search: |
;310/40MM,306-309
;200/181,600,343,339 ;60/516,527 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nguyen; Tuyen T
Attorney, Agent or Firm: Madson & Metcalf
Claims
What is claimed is:
1. A micromechanism having a first stable configuration and a
second stable configuration, the micromechanism comprising: a base
member; a leg having a base end and a shuttle end; a pin joint
coupling the base member and the base end of the leg; a shuttle
configured to slide along a substantially linear path; and a pin
joint coupling the shuttle and the shuttle end of the leg.
2. The micromechanism of claim 1 wherein the pin joint coupling the
base end of the leg to the base member is a fixed pin joint.
3. The micromechanism of claim 1 wherein the pin joint coupling the
shuttle end of the leg to the shuttle is a floating pin joint.
4. The micromechanism of claim 1 wherein the base member is a
microchip substrate.
5. The micromechanism of claim 1 wherein the base member is fixed
to a microchip substrate.
6. The micromechanism of claim 2 wherein the leg has at least one
dimple elevating the leg from the substrate.
7. The micromechanism of claim 2 wherein the floating pin joint has
at least one dimple elevating the floating pin joint from the
substrate.
8. The micromechanism of claim 2 wherein the shuttle has at least
one dimple elevating the shuttle from the substrate.
9. The micromechanism of claim 1 wherein the leg is a compliant
member.
10. The micromechanism of claim 1 wherein the leg is arched.
11. The micromechanism of claim 1 wherein the leg is substantially
straight.
12. The micromechanism of claim 1 wherein the leg is generally "V"
shaped.
13. The micromechanism of claim 1 wherein the leg deforms at a
toggle point.
14. The micromechanism of claim 1 wherein the micromechanism is
actuated by applying a rotational force at the pin joint.
15. The micromechanism of claim 1 wherein the micromechanism is
actuated by applying linear force to the shuttle.
16. A micromechanism having a first stable configuration and a
second stable configuration, the micromechanism comprising: a first
base member; a second base member; a first leg having a base end
and a shuttle end, wherein the base end of the first leg is coupled
to the first base member by a pin joint; a second leg having a base
end and a shuttle end, wherein the base end of the second leg is
coupled to the second base member by a pin joint; and a shuttle
having a first attachment location and a second attachment
locations, wherein the shuttle end of the first leg is coupled to
the first attachment location of the shuttle via a floating pin
joint and the shuttle end of the second leg is attached to the
second attachment location of the shuttle via a floating pint
joint.
17. The micromechanism of claim 16 wherein the first and second
legs are arched.
18. The micromechanism of claim 17 wherein the curvature of the
arched legs has a substantial constant radius.
19. The micromechanism of claim 17 wherein the curvature of the
first and the second legs at the first stable configuration is
substantially the same as the curvature of the first and second
legs at the second stable configuration.
20. The micromechanism of claim 16 wherein the first base member
and the first leg are substantially symmetric about the shuttle to
the second base member and the second leg.
21. The micromechanism of claim 16 wherein the first attachment
location and second attachment location at the same position on the
shuttle.
22. The micromechanism of claim 16 wherein the shuttle end of the
first leg and the shuttle end of the second leg are coupled to the
same floating pin joint.
23. The micromechanism of claim 16 wherein the mechanism is toggled
from the first stable configuration to the second stable
configuration by a thermal actuator operably connected to the
shuttle.
24. The micromechanism of claim 16 wherein the mechanism is toggled
from the first stable configuration to the second stable
configuration by an electrostatic actuator operably connected to
the shuttle.
25. The micromechanism of claim 16 wherein the shuttle has a
guiding slot and a guiding mount that are configured to maintain a
substantially linear travel of the shuttle.
26. The micromechanism of claim 16 wherein the shuttle has a
toothed extension extending away from the center of the
micromechanism, the toothed extension being engaged by at least one
gear configured to rotatably drive the toothed extension in order
to toggle the micromechanism between stable configurations.
27. The micromechanism of claim 25 wherein the gear has a center
hub and the gear is rotated by a thermal actuator tangentially
coupled to the center hub.
28. The micromechanism of claim 16 wherein the shuttle is
configured to open a circuit in one stable configuration and close
the circuit in the other stable configuration.
29. A micromechanism having a first stable configuration and a
second stable configuration, the micromechanism comprising: a base
member; a compliant leg having a base end and a shuttle end,
wherein the base end of the compliant leg is integrally connected
to the base member via a compliant flexible pivot; and a solid
shuttle coupled to the shuffle end of the compliant leg via a
floating pin joint, wherein the solid shuttle is configured to
slide along a substantially linear path.
30. The micromechanism of claim 29 wherein the compliant flexible
pivot is a small length flexural pivot.
31. A micromechanism having a first stable configuration and a
second stable configuration, the micromechanism comprising: a base
member; a compliant leg having a base end and a shuttle end,
wherein the base end of the compliant leg coupled to the base
member via a pin joint; and a solid shuttle integrally formed to
the shuttle end of the compliant leg via a compliant flexible
pivot.
32. The micromechanism of claim 31 wherein the compliant flexible
pivot is a small length flexural pivot.
33. A micromechanism having a first stable configuration and a
second stable configuration, the micromechanism comprising: a first
base member; a second base member; a first set of arched legs each
leg has a base end and a shuttle end, wherein the base ends of the
first set of arched legs are coupled to the first base member by a
plurality of pin joints; a second set of arched legs each leg has a
base end and a shuttle end, wherein the base ends of the second set
of arched legs are coupled to the second base member by a plurality
of pin joints; and a shuttle having a first attachment side and a
second attachment side, wherein the shuttle ends of the first set
of arched legs are coupled to the first attachment side of the
shuttle via a plurality of floating pin joints and the shuttle ends
of the second set of arched legs are attached to the second
attachment side of the shuttle via a plurality of floating pin
joints.
Description
FIELD OF THE INVENTION
The present method and apparatus relates to dual position
mechanisms. More particularly, the invention relates to compliant
bistable mechanisms, and the invention also relates to an apparatus
and method for a dual position latching mechanism.
TECHNICAL BACKGROUND
The term "compliant mechanisms" relates to a family of devices in
which integrally formed flexural members provide motion through
deflection. Such flexural members may therefore be used to replace
conventional multi-part elements such as pin joints. Compliant
mechanisms provide several benefits, including backlash-free,
wear-free, and friction-free operation. Moreover, compliant
mechanisms significantly reduce manufacturing time and cost.
Compliant mechanisms can replace many conventional devices to
improve functional characteristics and decrease manufacturing
costs. Assembly may, in some cases, be obviated entirely because
compliant structures often consist of a single piece of
material.
In microelectromechanical systems (MEMS), compliant technology
allows each mechanism of a MEMS system to be an integrally formed,
single piece mechanism. Because MEMS devices are typically made by
a layering and etching process, elements in different layers must
normally be etched and formed separately from each other.
Additionally, elements with complex shapes, such as pin joints,
require multiple steps and layers to create the pin, the head, the
pin-mounting joint, and the gap between the pin and the surrounding
ring used to form the joint. While pin joints do have difficulties
in manufacturing, these complex shapes do have advantages of
allowing large displacements and low stresses compared to fully
compliant mechanisms.
An integrally formed compliant mechanism, on the other hand, may be
constructed as a single piece, and may even be constructed in
unitary fashion with other elements of the micromechanism.
Substantially all elements of many compliant devices may be made
from a single layer. Reducing the number of layers, in many cases,
simplifies the manufacturing and design of MEMS devices. Compliant
technology also has unique advantages in MEMS applications because
compliant mechanisms can be manufactured unitarily, i.e., from a
single continuous piece of material, using masking and etching
procedures similar to those used to form semiconductors.
In MEMS as well as in other applications, there exists a large need
for "bistable devices," or devices that can be selectively disposed
in either of two different, stable configurations. Bistable devices
can be used in a number of different mechanisms, including
switches, valves, clasps, and closures. Switches, for example,
often have two separate states: on and off. However, most
conventional switches are constructed of rigid elements that are
connected by hinges, and therefore do not obtain the benefits of
compliant technology. Compliant bistable mechanisms have particular
utility in a MEMS environment, in which electrical and/or
mechanical switching at a microscopic level is desirable, and in
which conventional methods used to assemble rigid body structures
are ineffective.
Bistable mechanisms present a unique challenge because the
compliant elements must be properly balanced so that two fully
stable positions exist. Even if a bistable design is obtained by
fortunate guesswork or extensive testing, conventional optimization
techniques are often ineffective because the design space is so
complex, i.e., highly nonlinear and discontinuous, with such a
small feasible space that gradient-driven methods are unable to
reach a workable solution. The likelihood that a stochastic method
will stumble onto a solution is extremely small in fully compliant
designs. Hence, it is difficult to enhance the fully compliant
bistable designs, except through additional experimentation.
However, implementation of designs that allow for large
displacements of bistable mechanisms can provide for mechanisms
that are more predictable and require less experimentation to
obtain two stable configurations. Adding pin joints to compliant
mechanisms can allow for these large displacements to enable
bistability without undue experimentation and analysis.
Unfortunately, previous MEMS bistable designs have encountered
difficulties with applying pin joints to non-stationary members.
Additionally, various attempts of using non-stationary pin joints
have encountered motion problems as the result of stiction, the
bonding of moveable members to the microchip substrate.
Consequently, it would be an advancement in the art to provide a
bistable compliant mechanism, and particularly a bistable compliant
mechanism that would have a large displacement to ease design
considerations as well as a bistable mechanism that can employ pin
joints on moveable structures.
Another problem in the art of bistable and dual positional
mechanisms is the inability of these mechanisms to sustain a force
that is greater than the force that actuates the mechanism into its
stable configurations. To obtain a highly stable mechanism, the
mechanism should have the ability to lock to one of two positions.
One such stable device is a latching mechanism. Most latching
mechanisms provide for interference engagements between two members
that will maintain a force larger than the engagement force.
However in creating a highly secure and stable configuration, these
latching mechanisms often require multiple actuators to both latch
and unlatch the mechanism. Further, complex processes and
operations are needed to operate these mechanisms that limit the
number of applications for latching mechanisms, especially MEMS
applications. This subsequently increases the cost and size of the
mechanism.
Consequently, it would be an advancement in the art to provide a
latching mechanism that could lock and unlock through the use of a
single actuator. The latch should also be able to sustain a force
larger than the force used to lock the latching mechanism as well
as be easy to unlatch.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a micromechanism having a first
stable configuration and a second stable configuration. The
micromechanism comprises a complaint leg, a base member, and a
shuttle. The complaint leg has a base end and a shuttle end,
wherein the base end is coupled to the base member via a pin joint
and the shuttle end is coupled to the shuttle via a pin joint. In
one embodiment, the pin joint that couples the compliant leg to the
base member is a fixed pin joint and the pin joint that couples the
compliant leg to the shuttle is a floating pin joint.
The bistable micromechanism may be located on a microchip substrate
where the base member is fixed to the microchip substrate. The
bistable mechanism may further have a plurality of dimples that
extend from the bottom of the mechanism. The dimples are configured
to elevate the mechanism above the substrate to prevent stiction.
The dimples may be located on the floating pin joint, the shuttle,
or the leg.
The leg may have any number of shapes to allow the mechanism to be
bistable. The leg may be arch, straight, or "V" shaped. Other
shapes are possible so long as the shape functions similar to a
spring by storing potential energy when compressed. The mechanism
operates by increasing potential energy in the leg as it is
deflected toward the maximum potential energy position. From the
maximum potential energy position, the mechanism may toggle in one
of two directions toward one of two low potential energy positions.
Thus, the leg may toggle between low potential energy positions,
where these two low potential energy positions are separated by the
maximum potential energy position.
Another embodiment of the present invention provides for a latching
mechanism comprising a grasping member, a lock slider, and a detent
slider. The lock slider is configured to induce a locking
deflection with respect to the grasping member to reach an engaged
position. The lock slider is also capable of inducing an unlocking
deflection with respect to the grasping member, where the unlocking
deflection is greater than the locking deflection. The detent
slider is coupled to the lock slider to selectively maintain the
unlocking deflection with respect to the grasping member. This
unlocking deflection allows the lock slider to disengage the
grasping member and retract to its initial position.
The grasping member may be a compliant mechanism that has a fixed
end and a free end that are separated by a generally flexible arm.
The free end comprises an engagement member and a disengagement
member. The engagement member is configured to engage the lock
slider in a locked configuration and the disengagement member is
configured to engage the lock slider in an unlocked configuration.
The detent slider is operably connected to the lock slider. The
lock slider is substantially situated with the perimeter of the
detent slider and the detent slider has a raised member that
engages a stop that is situated on top of the lock slider. Thus act
the lock slider moves, the detent slider will react to its
movements as the stops abut the raised member. The mechanism is
capable of being actuated by a thermal in-plane microactuator in a
MEMS application. The actuator can both lock and unlock the
latching mechanism by driving the lock slider in a single
direction.
This latching mechanism follows the process of displacing the lock
slider a first distance in an actuation direction sufficient to
engage a grasping member in a locked configuration. Then the step
of displacing the lock slider a second distance in the actuation
direction sufficient to deflect the grasping member in an unlocked
configuration is performed. Once the grasping members are deflected
the step of displacing the lock slider a third distance in the
actuation direction sufficient to maintain the grasping member in
the unlocked configuration occurs. Then finally, the step of
displacing the lock slider a fourth distance in a direction
opposite the actuation direction, wherein the third distance is
sufficient to disengage the grasping member finishes the
processes.
Numerous other embodiments of the bistable mechanism and the
latching mechanism may be created through varying parameters of the
mechanism. For example, additional leg sets may be added to the
bistable mechanism and the type of joints in the mechanism can be
varied for different applications. In a latching mechanism the
members that induced the locked and unlocked configurations may be
varied to create a design that is capable of being placed in a wide
variety of locations.
DESCRIPTION OF DRAWINGS
FIG. 1 is a plan view of one embodiment of a compliant bistable
mechanism according to the invention;
FIG. 2 is a plan view of an analytical model to approximate the
operation of the bistable mechanism of FIG. 1;
FIG. 3 is a flowchart diagram showing one embodiment of an
optimization process for compliant mechanisms;
FIG. 4 is a graph showing a local optimum and a global optimum for
an objective characteristic to be optimized over a single
analytical model characteristic;
FIG. 5 is a flowchart diagram showing one embodiment of a first
recursive optimization algorithm suitable for the optimization
process of FIG. 3;
FIG. 6 is a flowchart diagram showing one embodiment of a second
recursive optimization algorithm suitable for the optimization
process of FIG. 3;
FIG. 7 is a plan view of an alternative embodiment of a compliant
bistable mechanism according to the invention;
FIG. 8 is a plan view of another alternative embodiment of a
compliant bistable mechanism according to the invention;
FIG. 9 is a plan view of yet another alternative embodiment of a
compliant bistable mechanism according to the invention; and
FIG. 10 is a plan view of still another alternative embodiment of a
compliant bistable mechanism according to the invention.
FIG. 11 is a plan view of one embodiment of a compliant
pined-pinned bistable mechanism according to the invention;
FIG. 12 is a plan view of an alternative embodiment of a
non-actuated compliant pined-pinned bistable mechanism according to
the invention;
FIG. 13 is a plan view of an alternative embodiment of an actuated
compliant pined-pinned bistable mechanism according to the
invention;
FIG. 14 is a plan view of an alternative embodiment of a
non-actuated compliant pined-pinned bistable mechanism attached to
a gear actuator;
FIG. 15 is a plan of one embodiment of a latching mechanism
according to the invention;
FIG. 16 is an operational plan view of an alternative embodiment of
the latching mechanism according to the invention;
FIG. 17 is an operational plan view of an alternative embodiment of
the latching mechanism attached to an amplified thermal in-plane
microactuator; and
FIG. 18 is an isometric view of an alternative embodiment of the
latching mechanism according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
The present apparatus and method will be best understood by
reference to the drawings, wherein like parts and steps are
designated by like numerals throughout. It will be readily
understood that the components of the present mechanism, as
generally described and illustrated in the Figures herein, could be
arranged and designed in a wide variety of different
configurations. Thus, the following detailed description of the
embodiments of the apparatus and method, as represented in the
Figures, are not intended to limit the scope of the claim, but are
merely representative of present embodiments of the apparatus and
method.
Referring to FIG. 1, one example of an integrally formed compliant
mechanism 10, or mechanism 10, is shown. The mechanism 10 may be
sized for MEMS applications. Although many of the examples
presented herein apply to MEMS applications, the apparatus and
method of the present invention are not limited to MEMS, but are
rather applicable to compliant mechanisms in general.
The exemplary mechanism 10 of FIG. 1 is a bistable micromechanism,
or a MEMS device that can be actuated between two stable
configurations through the application of an input force 11. Such a
mechanism may be used to perform microswitching functions or the
like. The mechanism 10 may have a longitudinal direction 12, a
lateral direction 14, and a transverse or out-of-plane direction
16. The mechanism 10 may have a substantially planar configuration,
e.g., all parts of the mechanism 10 may have substantially the same
thickness and positioning in the transverse direction 16. The
mechanism 10 may have a shuttle 20 configured to receive the input
force 11 and, if desired, exert an output force on some other
object.
The shuttle 20 may be connected to a first base member 22, a second
base member 24, a third base member 26, and a fourth base member
28. The base members 22, 24, 26, 28 may be stationary, or may be
affixed to other stationary or mobile MEMS devices. Consequently,
the base members 22, 24, 26, 28 are depicted simply as attachment
surfaces. The first and third base members 22, 26 may be separated
from the second and fourth base members 24, 28 by an offset
distance 29. The offset distance 29 may be substantially fixed. The
shuttle 20 may be connected to the base members 22, 24, 26, 28
through the use of a first leg 30 and a second leg 32. The legs 30,
32 may be thick enough to be substantially rigid. The exemplary
mechanism 10 of FIG. 1 implements two general types of compliant
segments, or segments that are designed to provide motion and/or
biasing force through deformation.
More specifically, the mechanism 10 may have a first shuttle pivot
coupling 40 and a second shuttle pivot coupling 42 that pivotally
attach the shuttle 20 to the first and second legs 30, 32.
Similarly, the mechanism may have a first base pivot coupling 44
and a second base pivot coupling 46 that pivotally attach the first
and second legs 30, 32 with the base members 22, 24, 26, 28. As
shown, the pivot couplings 40, 42, 44, 46 take the form of
small-length flexural pivots 40, 42, 44, 46, or flexural pivots 40,
42, 44, 46; however, in other embodiments, pin joints or other
types of compliant members may be used. The flexural pivots 40, 42,
44, 46 allow the shuttle 20 to travel from a first position 50 to a
second position 52 by flexing to provide pivotal motion similar to
that of a pin joint. Thus, the mechanism 10 has a first stable
configuration 54, or first configuration 54 corresponding to the
first position 50 and a second stable configuration 56, or second
configuration 56 corresponding to the second position 52.
Generally, small-length flexural pivots are thin cross-sectioned
segments that replace traditional pivotal joints while still
allowing the joint to be mathematically modeled as a traditional
pivotal joint. Small-length flexural pivots bend along their length
to allow other elements of a micromechanism to move relative to
each other. Small-length flexural pivots can have a wide variety of
lengths and shapes to suit multiple designs. Longer small-length
flexural pivots allow for a large range of motion, while shorter
pivots are easier to model with techniques, such as pseudo-rigid
body modeling.
To facilitate mathematical modeling of the small-length flexural
pivots through methods such as pseudo-rigid body modeling, it is
advantageous to form each of the flexural pivots 40, 42, 44, 46
with a length of less than 10% of the length of the legs 30, 32 to
which they are attached. However, the length of the flexural pivots
40, 42, 44, 46 must also be sufficiently long to allow the legs 30,
32 to rotate through the necessary angle as the shuttle 20 travels
between the first and second positions 50, 52. Therefore, depending
on the desired displacement between the first and second positions
50, 52 of the shuttle 20, a 10% ratio of flexural pivot length to
leg length may be advantageous. Longer flexural pivots 40, 42, 44,
46 may also be used, but may require the use of more advanced
modeling techniques.
The first and third base members 22, 26 may be connected together
by a first mounting beam 58, and the second and fourth base members
24, 28 may be connected together to form a second mounting beam 59.
The mounting beams 58, 59 may have a length and thickness selected
to permit bending in the fixed-fixed configuration. Thus, the first
and third base members 22, 26 may operate in conjunction with the
first mounting beam 58 to form a first deformable mount 60, and the
second and fourth base members 24, 28 may similarly operate in
conjunction with the second mounting beam 59 to form a second
deformable mount 62. The first and second deformable mounts 54, 56
may be coupled to the legs 30, 32 by the first and second base
flexural pivots 44, 46, respectively. The deformable mounts 60, 62
may function similar to springs, in that they elastically deflect
when the legs 30, 32 press outward against them.
The motion of the elements of a compliant mechanism is determined
by the geometry of the elements. Thin or necked-down members, such
as the deformable mounts 60, 62 and the flexural pivots 40, 42, 44,
46, will flex as they receive a load sufficient to cause a
deformation or a deflection. Conversely, thick members, such as the
legs 30, 32 and the shuttle 20, will remain substantially
undeflected under loading of the mechanism 10. Typically, some
minor bending will occur in thicker members such as the legs 30, 32
and the shuttle 20; however, such bending is small in comparison to
the deflections of the thinner members. The combination of the
flexural pivots 40, 42, 44, 46 and deformable mounts 60, 62 with
the legs 30, 32 provides the range of motion necessary for the
mechanism 10 of FIG. 1 to move between the first configuration 54
and the second configuration 56.
The deformable mounts 60, 62 may be undeflected, or only slightly
deflected, when the shuttle 20 is in the first position 50 or the
second position 52 so that the first and second configurations 54,
56 are both low potential energy states. However, when the shuttle
20 is disposed between or outside the first and second positions
50, 52, the deformable mounts 60, 62 may be deformed to a larger
extent to store a larger amount of potential energy, and thereby
provide the impetus for the mechanism 10 to return to the first
configuration 54 or the second configuration 56.
Thus, the mechanism 10 obtains its stability in two configurations
from the existence of two low potential energy positions. A
mechanism implementing low potential energy positions provides
better control and a larger range of design possibilities than do
bistable mechanisms implementing residual stress or buckled beamed
methods. The mechanism 10 of FIG. 1 uses a combination of the
flexural pivots 40, 42, 44, 46, the deformable mounts 60, 62, and
the legs 30, 32 to create at least two low potential energy
positions.
When the shuttle 20 is disposed between the first and second
positions 50, 52, the deformable mounts 60, 62 may be bent outward.
When the shuttle 20 is disposed outward of the first position 50 or
the second position 52, the deformable mounts 60, 62 may be bent
inward. Deformable mounts need not be configured in the same manner
as the deformable mounts 60, 62 of FIG. 1, but may involve the use
of fixed-free cantilever mounting beams, zigzagging flexural
segments, or the like, as will be shown and described
hereafter.
The mechanism 10 may also be described as a compliant bridge 70
coupled to and integrally formed with the base members 22, 24, 26,
28. The bracket labeled 70 indicates that, in the mechanism 10 of
FIG. 1, the compliant bridge 70 includes the shuttle 20, the
flexural pivots 40, 42, 44, 46, and the legs 30, 32.
The compliant bridge 70 may be selectively disposable along a first
path 72, which corresponds to the first position 50 and the first
configuration 54, and a second path 74, which corresponds to the
second position 52 and the second configuration 56. The paths 72,
74 may each be longer than the offset distance 29, so that the
compliant bridge 70 is curved or kinked in each of the first and
second configurations 54, 56. Conversion between the first and
second configurations 54, 56 may simply entail reversing the
curvature or kinking of the compliant bridge 70.
The compliant bridge 70 is curved or kinked in both configurations
54, 56 because the tendency of the deformable mounts 60, 62 to stay
straight is of a higher magnitude than the tendency for the
compliant bridge 70 to return to its original state. For example,
the mechanism 10 may be manufactured in the first configuration 54,
so that there is substantially no deformation of the mechanism 10
in the first configuration 54. Thus, in the second configuration
56, the compliant bridge 70 may be generally bent in a direction
opposite to its original, undeflected curvature. The compliant
bridge 70 may thus exert outward force against the deformable
mounts 60, 62 in the second configuration 56 due to its tendency to
return to its undeflected state. The deformable mounts 60, 62 must
therefore provide a resilient force sufficient to counteract the
outward pressure of the compliant bridge 70 in the second
configuration 56, so that the compliant bridge 70 will remain
deflected in the absence of any external force.
Such tendencies or strengths are a function of the geometry and
positioning of the elements of the mechanism 10. In FIG. 1, the
deformable mounts 60, 62 have a thicker width than the flexural
pivots 40, 42, 44, 46, so that the deformable mounts 60, 62 have a
comparatively strong tendency to remain straight. The resilient
forces produced by the deformable mounts 60, 62 and the flexural
pivots 40, 42, 44, 46 can be compared to springs with different
spring constants. Thicker elements are analogous to springs with
large spring constants, and therefore resist deformation more than
elements that would be modeled with a smaller spring constant.
The compliant bridge 70 may have a first beam section 80 that
generally encompasses the first leg 30, the first shuttle flexural
pivot 40, and the first base flexural pivot 44. Similarly, the
compliant bridge 70 may have a second beam section 82 that
generally encompasses the second leg 32, the second shuttle
flexural pivot 42, and the second base flexural pivot 46. The
compliant bridge 70 may also have a central portion 84 that
includes the shuttle 20.
The curvature of the paths 72, 74 may be somewhat exaggerated in
the view of FIG. 1 to distinctly show the first and second
configurations 54, 56; the paths 72, 74 may, in reality, be nearly
straight. The curvature of the paths 72, 74 may be adjusted to suit
the desired force and displacement characteristics of the mechanism
10. Additionally, multiple other factors may also be adjusted to
modify the operation of the mechanism 10.
When the input force 11 is applied to the shuttle 20, the shuttle
20 is moved toward the second position 52, thereby pressing the
deformable mounts 60, 62 outward. The deformable mounts 60, 62 flex
outward to accommodate the increased length of the compliant bridge
70 as the compliant bridge 70 deflects toward a straight
configuration. The potential energy present in the mechanism 10
increases as the legs 30, 32 approach a linear alignment; maximum
potential energy may be reached at or near the point at which the
compliant bridge 70 becomes completely straight.
The maximum potential energy position is the toggle point. At the
toggle point, the compliant bridge 70 is in an unstable
equilibrium, in which the compliant bridge 70 is equally biased
between the first and second configurations 54, 56, each of which
has a low potential energy. A slight displacement toward either of
the configurations 54, 56 will snap the compliant bridge 70 into
one of the configurations 54, 56. If continued force is applied in
the direction indicated by the input force 11, the compliant bridge
70 will be urged to bend by the deformable mounts 60, 62 as the
deformable mounts 60, 62 relax into a comparatively straight,
undeformed, configuration to provide the second stable
configuration 56. The deformable mounts 60, 62 may not fully relax
in the second configuration 56 due to the continued outward force
exerted by the compliant bridge 70.
To actuate the mechanism 10 back to the first configuration 54, a
return force, or a load sufficient to deflect the compliant bridge
70 beyond the toggle point, towards the first stable position 54,
need only be applied in a direction opposite to that of the input
force 11. The magnitude of the return force required to return the
mechanism 10 to the first configuration 54 need not be equal to the
magnitude of the input force 11 required to actuate the mechanism
10 into the second configuration 56. Indeed, the input force 11 and
the return force may be specifically designed to suit the
application in which the mechanism 10 is used.
Through the use of compliant technology, a bistable mechanism may
be produced without conventional, separate members and joints. The
functions of such members and joints are instead carried out by
integrally formed elements that allow for motion similar to that of
conventional mechanism. While a compliant structure can provide
motion and displacement similar to that of designs involving
conventional rigid elements, the design process for a compliant
mechanism has obstacles not present in the case of conventional
mechanisms utilizing separate, rigid parts. For example, the
deformable mounts 60, 62 not only serve as spring-type elements to
bias the shuttle 20 toward the first position 50 or the second
position 52, but they also function as attachments for the first
and second base flexural pivots 44, 46. Thus, multiple forces and
torques simultaneously act on the deformable mounts 60, 62.
Additionally, comparatively large deflections may occur.
As a result, determining how the material flexes requires complex
non-liner equations. The complexity of these equations makes it
difficult to obtain closed form mathematical relationships between
geometric characteristics of the mechanism 10 and the resulting
operational characteristics. "Geometric characteristics" refers to
physical properties of a compliant structure, including member
dimensions, member positions, and material properties. Hence, with
traditional methods, it is difficult to create a compliant
structure that functions in the desired manner, let alone optimize
the structure for a desired function. As mentioned previously, the
present invention presents a system and method whereby compliant
structures in general can be designed and optimized without the
computationally intensive procedures that have been necessary in
the past.
More specifically, the process of designing and optimizing a
compliant structure can be simplified by modeling a compliant
structure as a mechanism with rigid members connected with
conventional joints and springs. Such a model may be called a
"pseudo-rigid body model," which will be referred to as an
analytical model in the following discussion.
Referring to FIG. 2, an analytical model 110 of the mechanism 10 of
FIG. 1 is depicted. Each elements of the mechanism 10 is present in
the analytical model 110. More specifically, the input force 11 may
be modeled as a longitudinal spring 111 with a linear
configuration. Such a force may be applied by an actuator affixed
to the shuttle 20, which may resist longitudinal motion of the
shuttle 20 in either direction until the actuator is triggered.
However, if the input force 11 does not vary in linear fashion with
the displacement of the shuttle 20, some other model may be more
appropriate. For example, if the shuttle 20 is part of an
accelerometer and is actuated only by its own weight, the
longitudinal spring 111 may be removed entirely from the analytical
model 110, or negated by setting its spring constant to zero. The
shuttle 20 may be represented by a longitudinal slider 120 that
moves only in the longitudinal direction 12 by virtue of the
symmetry of the model 110.
The legs 30, 32 may be modeled as legs 130, 132, which are
connected by pin joints and torsional springs. More precisely, the
first and second shuttle flexural pivots 40, 42 may be modeled with
a single pin joint/torsional spring combination 140 on the slider
120. The torsional spring of the pin joint/torsional spring
combination 140 represents the resistance of the shuttle flexural
pivots 40, 42 to bending. The first and second base flexural pivots
44, 46 may be modeled as first and second pin joint/torsional
spring combinations 144, 146 attached to the legs 130, 132. The
torsional springs of the pin joint/torsional spring combinations
144, 146 represent the resistance of the base flexural pivots 44,
46 to bending.
The resilient force of the first mounting beam 58 may be
represented by a first lateral spring 155, and the resilient force
of the second mounting beam 59 may be represented by a second
lateral spring 157. The pin joint/torsional spring combinations
144, 146 may be attached to first and second lateral sliders 158,
159, respectively, which represent the physical attachment provided
by the first and second mounting beams 58, 59. The lateral sliders
158, 159 may be constrained to move in the lateral direction 14 by
the longitudinal symmetry of the deformable mounts 60, 62. The
combination 160 of the first lateral spring 155 with the first
lateral slider 158 may be analogous to the first deformable mount
60, and the combination 162 of the second lateral spring 157 with
the second lateral slider 159 may be analogous to the second
deformable mount 162.
The analytical model 110 has many "analytical model
characteristics," each of which can be changed to alter the
operational characteristics of the model 110. The analytical model
characteristics are analogous to the geometric characteristics of
the compliant structure. For example, the legs 130, 132 each have a
length and a rest angle with respect to the lateral direction 14.
Each of the pin joint/torsional spring combinations 140, 144, 146
may have a spring constant that indicates the strength of the
torsional spring. Each of the linear springs 111, 155, 157 may also
have spring constants. Mathematical relationships between the
analytical model characteristics and operational characteristics of
the analytical model 110 may be determined using traditional tools
of kinematic analysis. The analytical model characteristics may be
altered to simulate different configurations of the mechanism 10 in
its compliant form.
This type of pseudo-rigid body modeling can be applied to many
different compliant structures besides bistable micromechanisms.
After creating an analytical model of the compliant structure,
conventional techniques can be applied to the analytical model to
obtain closed form equations that relate operational
characteristics to analytical model characteristics, such as the
dimension, orientation, stress, force, thickness, or width. When
the desired analytical model characteristics have been determined,
a compliant design may be produced so that comparable operational
characteristics can be obtained. This process of creating an
analytical model of a compliant structure and then characterizing
the structure with conventional rigid body equations allows for a
large number of candidate designs to be considered for any given
application. Additionally, once a feasible analytical model is
determined, the model may be optimized to make the structure
perform a specific function in a predetermined manner.
The initial step in optimizing a compliant structure is to
determine the desired operational characteristics of the mechanism.
For example, the maximum stress on the structure elements, such as
the small-length flexural pivot, must be lower than the yield
strength of the material to prevent failure. As another example, it
may be desirable to minimize an input force, maximize an output
force, maximize an output displacement, or obtain some other
objective characteristic.
The mechanism 10 in FIG. 1 may be designed through the use of such
an optimization process. The mechanism 10 has several geometric
characteristics that must be considered when performing an
optimization process. First, the mechanism 10 is to be stable in
two different configurations 54, 56. Bistable design can be
difficult to achieve because of the complexity inherent in
compliant mechanisms; the interactions of flexible members,
analysis of large deformations, and the like make it difficult to
determine which sets of geometric characteristics will provide a
bistable design. However, through the use of an analytical model
like that of FIG. 2, multiple bistable configurations may be
found.
More specifically, certain ranges of analytical model
characteristics may be determined to yield bistable operation; such
ranges may then form the parameters of further analysis to select
the best specific configuration. Which bistable configuration is
the best depends on the desired operational characteristics. One
operational characteristic may be selected and designated an
"objective characteristic," or the operational characteristic that
is to be obtained through the optimization process. The objective
characteristic may be a target value, such as a desired threshold
input force to move the mechanism 10 from the first configuration
54 to the second configuration 56. In the alternative, the
objective characteristic may be a value that is to be maximized or
minimized; for example, the displacement of the shuttle 20 between
the first and second positions 50, 52 may be minimized.
Referring to FIG. 3, a flowchart depicts one example of an
optimization process 210 according to the present invention. As
mentioned previously, the optimization process 210 is applicable
not only to bistable mechanisms or MEMS, but can be used for
compliant mechanisms in general. As described previously, the first
step may be to select 212 a compliant structure, such as the
mechanism 10 of FIG. 1, and an objective characteristic to be
optimized. For the mechanism 10, the objective characteristic may
be the displacement between the first and second positions 50, 52
of the shuttle 20. Alternatively, a plurality of objective
characteristics may be selected and simultaneously optimized.
After the compliant structure and the objective characteristic have
been chosen, an analytical model, such as the model 110 of FIG. 2,
may be created 214. Traditional analysis of rigid body members may
be used to obtain mathematical relationships that relate the
objective characteristic to characteristics of the analytical
model, such as member lengths and angles, spring constants, and the
like. Such mathematical relationships may consist of closed form
equations that can be readily applied by a computer in an iterative
process.
Alternatively, a compliant structure may be optimized without using
an analytical model if a different form of analysis is used. For
example, the compliant structure may be modeled by computer through
the use of finite element analysis or a similar method. Finite
element analysis creates a geometric model of the compliant
structure by dividing the compliant structure into a large number
of small geometric shapes, such as tetrahedrons. A computer then
utilizes an iterative process involving simultaneous sets of
equations to determine how the structure will respond to loads.
Thus, the finite element method may be used to evaluate multiple
configurations of the selected compliant structure without creating
closed form mathematical relationships. However, finite element
analysis is computationally intensive, and would have to be
performed with each iteration of an optimization algorithm.
Consequently, optimization through finite element analysis may be
too time consuming to be practical. Therefore, the following
discussion assumes the use of an analytical model.
Returning to FIG. 3, once the analytical model has been created
214, initial values of the characteristics of the analytical model
should be selected 216. The initial values may simply be a guess as
to what may be close to the optimal values of the analytical model
characteristics; such a guess may be made through analysis of the
model, experimentation, or experience.
A first recursive optimization algorithm may then be applied 222 to
the analytical model. In general, the first recursive optimization
algorithm takes the initial set of values for the analytical model
characteristics and performs an iterative process to approach a
global optimum, or a set of analytical model characteristics that
will produce the most desirable value of the objective
characteristic. In the exemplary process 210 of FIG. 4, the main
purpose of applying 222 the first recursive optimization algorithm
is not necessarily to find the global optimum itself, but to find
the general region in which the global optimum lies among local
optima. This concept will be illustrated with greater clarity in
FIG. 4.
The first recursive optimization algorithm may return a first set
of values of the analytical model characteristics; the first set of
values bring the objective characteristic near a global optimum. A
second recursive optimization algorithm may then be applied 224.
The second recursive optimization algorithm may receive the first
set of values of the analytical model characteristics and may
perform iterative steps to obtain a second set of values of the
analytical model characteristics that provide a value of the
objective characteristic within a tighter threshold of the global
optimum. The threshold is necessary because the second recursive
optimization algorithm may otherwise come infinitely close to the
global optimum without actually reaching it.
Once the second set of analytical model characteristics has been
obtained, the analytical model characteristics are utilized to
derive 226 the geometric characteristics of the selected compliant
structure that will obtain a similar result. Derivation of the
geometric characteristics from the analytical model characteristics
may be accomplished by utilizing known relationships between
compliant structures and their rigid body approximations. For
example, a torsional spring constant from the analytical model 110
may be used to determine a thickness for a small-length flexural
pivot so that the small-length flexural pivot simulates the
torsional spring constant in operation. Other geometric
characteristics, such as member lengths, materials, member angles,
and the like may be determined in a similar manner, i.e., by
comparison with the second set of values of the analytical model
characteristics.
The optimization process 210 is only one example of an optimization
method according to the present invention; many other processes may
also be used. As mentioned above, a different method of analysis,
such as the finite element method, may be used in place of creating
214 the analytical model. Additionally, rather than applying 222 a
first recursive optimization algorithm and applying 224 a second
recursive optimization algorithm, a single optimization algorithm
may be used to approach the global optimum and come within the
threshold value.
Hence, steps of the optimization process 210 may generally be
omitted, modified, and/or added to create new embodiments. However,
the following discussion is based on the optimization process 210.
FIG. 4 is a graphical illustration of local and global optima; FIG.
5 provides additional detail regarding the operation of one
embodiment first recursive optimization algorithm, and FIG. 6
provides additional detail regarding the operation of one
embodiment of the second recursive optimization algorithm.
Referring to FIG. 4, a graph 230 shows the value of the objective
characteristic, mapped against the value of one analytical model
characteristic. Although optimization will most likely be carried
out by varying multiple analytical model characteristics, the
two-dimensional representation of FIG. 4 is somewhat easier to
describe and understand. Those of skill in the art will recognize
that the principles described below are equally applicable to
optimization processes in which multiple characteristics are
simultaneously changed.
The vertical axis represents the value of the objective
characteristic, such as the actuation force required to move the
shuttle 20 of the mechanism 10 of FIG. 1, between the first and
second positions 50, 52. In this embodiment, it is desirable for
the actuation force to be as low as possible. The horizontal axis
represents the value of the analytical model characteristic that is
to be varied to optimize the objective characteristic. The domain
depicted by the horizontal axis represents the feasible design area
for the analytical model characteristic that is to be varied.
As shown in FIG. 4, there are multiple valleys 232 in which
feasible designs come to relatively low (i.e., desirable) values of
the objective characteristic. One of the valleys 232 contains a
local optimum 234, which is a lowest value of the objective
characteristic within the valley 232 in which the local optimum 234
is present. The other valley 232 contains a global optimum 236,
which is a lowest value of the objective characteristic within the
entire feasible range of the analytical model characteristic. If a
high value of the objective characteristic were desirable, local
and global optima may be peaks instead of valleys.
If the optimization process is not robust enough, the optimization
algorithm may only obtain a local optimum, which would produce a
less desirable design. Many optimization algorithms tend to return
the optimum closest to the initial value provided to the algorithm.
Consequently, if the initial value of the analytical model
characteristic falls within the valley 232 in which the local
optimum 234 resides, such an optimization process would likely
return only the local optimum 234, without finding the global
optimum 236 that provides the best solution.
In order to avoid the local optimum problem, the optimization
process 210 of FIG. 3, applies 222 the first recursive optimization
algorithm primarily for the purpose of escaping from local optima,
such as the optimum 234. The optimization process 210 then applies
224 the second recursive optimization algorithm to find the value
of the analytical model characteristic that will be within a
smaller threshold of the global optimum 236.
Referring to FIG. 5, a more detailed flowchart depicts steps that
may be followed to apply 222 the first recursive optimization
algorithm. The first recursive optimization algorithm may be any
algorithm known in the art of mechanical design. As mentioned
previously, the first recursive optimization algorithm may be used
alone, if desired. The following discussion simply provides an
example of one first recursive optimization algorithm that may be
used in conjunction with a second recursive optimization algorithm
to obtain robust and accurate results.
More precisely, the first recursive optimization algorithm may
comprise a process known as simulated annealing. Other stochastic
methods, such as genetic algorithms, neural networks, and the like
may also be used; however, the following discussion assumes that
simulated annealing is the selected method. The simulated annealing
process utilizes random decision-making to ensure that the process
is able to move between the valleys 232. A first ending criterion
may first be selected 240. The first ending criterion may be a
required value of the objective characteristic that must be
obtained or passed in the positive or negative direction, a maximum
number of iterations, a maximum change in the objective
characteristic per iteration, or the like. An initial configuration
may then be designated 242 as the configuration with the initial
set of values that were selected 216 previously.
The initial configuration may be set 244 as the interim
configuration. The value of the objective characteristic 246 may
then be determined for the interim configuration. The value of the
objective characteristic may be obtained through the use of closed
form equations from an analytical model of the selected compliant
structure, from a computerized process such as finite element
analysis, or even through solving the complex equations involved
with direct analysis of the selected compliant structure.
Once the value of the objective characteristic has been determined,
the first recursive optimization algorithm may then determine 248
whether the first ending criterion has been achieved. As mentioned
above, the first ending criterion may take a wide variety of forms,
and may be tied to the value of the objective characteristic. If
the first ending criterion has been achieved, the first recursive
optimization algorithm may then set 250 the first values for the
analytical model characteristics as the values of the interim
configuration. The first values may then be returned by the first
recursive optimization algorithm.
If the first ending criterion has not been achieved, the first
recursive optimization algorithm may then randomly select 262 one
of the analytical model characteristics and change the selected
analytical model characteristic to form a changed interim
configuration. Not all of the analytical model characteristics need
be subject to change; some may be designated as characteristics to
be held constant. The magnitude of the change may also be randomly
determined if desired, or may be based in whole or in part on
factors such as the results of previous iterations, the type of
analytical model characteristic that has been selected at random,
or the like. The first recursive optimization algorithm may then
determine 264 whether the changed interim configuration provides a
better value of the objective characteristic than the original
interim configuration.
In order to determine 264 which configuration is preferable, the
value of the objective characteristic may be calculated or
retrieved, if it has already been determined and stored, for the
interim configuration and for the changed interim configuration.
For example, if the objective characteristic is minimization of the
actuation force, whichever configuration provides the lowest
actuation force provides the best value of the objective
characteristic.
If the changed interim configuration provides the better result,
the changed interim configuration may be unconditionally set 266 as
the new interim configuration. The old interim configuration may be
discarded. The value of the objective characteristic may then be
determined 246 with the new interim configuration to begin the
cycle again.
If the changed interim configuration does not provide the better
result, a probabilistic algorithm may be applied 268 to determine
whether the changed interim configuration should be kept. The
probabilistic algorithm may be as simple as the computer equivalent
of a coin toss, or may be based in whole or in part upon other
factors such as the difference between the values provided by the
two configurations, the history of the recursive process, or the
like. The first recursive optimization algorithm may determine 270
the results of the algorithm, and if the probabilistic algorithm
dictates that the changed interim configuration is to be kept, the
changed interim configuration may be set 266 as the new interim
configuration.
The probabilistic algorithm may also dictate that the changed
interim configuration should be discarded 272, in which case the
old interim configuration is kept, and the cycle may begin again.
Reiteration with the same interim configuration will not
necessarily yield the same result with each iteration because the
first recursive optimization algorithm may randomly select 262 the
analytical model characteristic to change, and possibly even the
magnitude of the change. In all likelihood, the interim
configuration will be redefined numerous times throughout the
optimization process. Once the first ending criterion has been met,
the first values 250 are set as the values of the interim
configuration.
The random acceptance or rejection of an inferior interim
configuration allows the first recursive optimization processes to
escape local optima. As can been seen in FIG. 4, were a
configuration to be within the valley 232 of a local optimum 234,
an optimization process may need to select a number of inferior
designs in order to find the global optimum 236. In the case of the
simulated annealing method, the algorithm that selects or rejects
an inferior design may be based upon a cooling schedule of metal.
The annealing processes would select fewer and fewer inferior
designs as the process cycled. The probabilistic algorithm applied
by the first recursive optimization algorithm may operate in a
similar manner.
After the first recursive optimization algorithm has been applied
222, a first set of values of the analytical model characteristics
may be returned by the first recursive optimization algorithm. The
first set of values may simply be one set of values that positions
the objective characteristic somewhere within the valley 232 in
which the global optimum 236 resides. The second recursive
optimization algorithm may then be applied 224 to obtain a second
set of values that are within a specified threshold of the global
optimum 236.
Referring to FIG. 6, a more detailed view of the operation of the
second recursive optimization algorithm is depicted. The second
recursive optimization algorithm need not be designed to avoid
local optima, but may simply operate to remain within the valley
232 in which the first values of the analytical model
characteristics lie. Consequently, gradient analysis may be
effectively used in conjunction with the second recursive
optimization algorithm. Consequently, the second recursive
optimization algorithm may comprise the generalized reduced
gradient method or a similar optimization process. Other
gradient-driven methods, such as sequential quadratic programming,
linear programming, and the like, may also be used, but the
following discussion assumes the use of the generalized reduced
gradient method.
The second recursive optimization algorithm may first receive 280
the first values of the analytical model characteristics, and
designate a second interim configuration as the configuration
having analytical model characteristics with the first values. A
second ending criterion may then be selected 282. Like the first
ending criterion, the second ending criterion may take a variety of
forms, and may be based upon the value of the objective
characteristic.
The second ending criterion may be somewhat more restrictive than
the first ending criterion; for example, the second ending
criterion may require a comparatively small threshold distance
between the global optimum 236 and the value of the objective
characteristic. Such a criterion may be measured, for example, by
measuring the differences between the values of the objective
characteristics in successive iterations. Very small differences
may indicate that the value of the objective characteristic that is
obtained is near the global optimum 236.
The second recursive optimization algorithm may then determine 284
which analytical model characteristics are to be kept constant
during iteration. Changing a larger number of the analytical model
characteristics may provide a better result because each additional
dimension of the analysis provides the possibility for a lower
global optimum. For example, if the graph 230 of FIG. 4 were
expanded to three dimensions, the new dimension may well provide a
global optimum more desirable than the global optimum 236 that is
available through variation of only one of the analytical model
characteristics. However, changing a smaller number of analytical
model characteristics may expedite the procedure, and may avoid
introducing geometric characteristics that are not viable from a
manufacturing standpoint.
The value of the objective characteristic may then be determined
286 with the second interim configuration. The second recursive
optimization algorithm may then determine 288 whether the second
ending criterion has been achieved. If so, the second values may be
set 290 as the values of the analytical model characteristics of
the second interim configuration. If the second ending criterion
has not been met, all of the values of the non-constant analytical
model characteristics may be changed to provide a second changed
interim configuration. The changes may have a random component, or
may be determined entirely by factors such as the effects of
changes in past iterations on the objective characteristic.
A vector may then be created 298 to describe the changes made to
the analytical model characteristics. The vector may take the form
of an ordered number set including all changes made. Properties of
the vector may be measured 300 to determine which changes are
improvements and which are not, e.g., which changes bring the
second changed interim configuration comparatively closer to the
global optimum 236. Such properties may be measured through the use
of partial derivatives; the partial derivative of each analytical
model characteristic with respect to the objective characteristic
indicates the effect that changes to that analytical model
characteristic have on the objective characteristic.
After the vector has been analyzed, the changes that have not had a
positive influence on the second interim configuration may be
discarded 302. The remaining changes may be incorporated 304 into
the second interim configuration to form a new second interim
configuration. Thereafter, the process may continue cyclically
until the second ending criterion has been achieved.
The result of the second recursive optimization algorithm is to
provide the second set of values of the analytical model
characteristics, which will provide the globally optimum value for
the objective characteristic within a comparatively tight
threshold. If desired, such a result could be obtained solely with
the first recursive optimization algorithm. However, the randomized
nature of the simulated annealing algorithm may make accurate
determination of the global optimum a comparatively time-consuming
process. Thus, the use of the second recursive optimization
algorithm may make the optimization process faster and more
accurate.
As mentioned previously, design and optimization methods presented
herein are applicable to a wide variety of compliant mechanisms
besides the mechanism 10 of FIG. 1. Additionally, bistable MEMS
devices according to the invention may be designed in other ways
besides those outlined in FIGS. 3, 5, and 6. Many bistable
configurations are possible aside from the mechanism 10 of FIG. 1.
Some such configurations will be shown and described in connection
with FIGS. 7 through 10.
Referring to FIG. 7, an alternative embodiment of a mechanism 310
with bistable properties is depicted; the mechanism 310 may also be
sized for MEMS applications. The mechanism 310 of FIG. 7 may have
elements similar to those of the mechanism 10 of FIG. 1; however,
the mechanism 310 may not have dual, laterally symmetrical
portions. The mechanism 310 may, for example, have a shuttle 320
disposed to move in the longitudinal direction 12, much like the
shuttle 20 of FIG. 1. The first and third base members 22, 26, the
first leg 30, the first shuttle flexural pivot 40, the first base
flexural pivot 44, and the first mounting beam 58 may be
substantially as shown and described in connection with FIG. 1. As
with FIG. 1, the first base member 22, the third base member 26,
and the first mounting beam 58 may form the first deformable mount
60.
The shuttle 320 may be integrally formed with and coupled to the
first shuttle flexural pivot 40. However, in place of the second
shuttle flexural pivot 42, the shuttle 320 may simply abut a
surface 321 against which the shuttle 320 is able to slide. Thus,
the lateral distance between the first deformable mount 60 and the
shuttle 320 is fixed. The shuttle 320 is constrained to move
longitudinally, like the shuttle 20 of FIG. 1; consequently, the
shuttle 320 may move in a manner similar to the shuttle 20.
The first deformable mount 60 may flex outward as the shuttle 320
moves toward the toggle point in order to accommodate the aligned
lengths of the shuttle 320, the first leg 30, and the flexural
pivots 40, 44. The shuffle 320 may be then snap into one of two low
potential energy positions as the first deformable mount 60 pushes
inward, toward its undeformed configuration. The mechanism 310 is
simple in design, and may be actuated between stable configurations
with about half the input force required to actuate the mechanism
10, assuming that the displacement of the shuttle 320 between low
potential energy positions is the same as that of the shuttle 20,
and that the surface 321 provides negligible friction. A low input
force may be beneficial for some applications, but may also cause
instability in other applications.
Stability is generally proportional to the force required to toggle
a bistable mechanism from one low potential energy configuration to
another low potential energy configuration. An embodiment requiring
a small force to toggle the mechanism is not as stable as a
mechanism that requires a large force. Nevertheless, a highly
stable mechanism will require a comparatively larger force to
actuate the mechanism between different stable configurations. A
high input force may place excessive energy burdens on a system,
especially in MEMS applications, in which energy consumption is
limited. In such applications, minimizing the toggle force may be
desirable.
However, stability may be compromised if the toggle force is too
low. For example, vibrations that occur from outside the system may
toggle a bistable mechanism with a small input force requirement.
Therefore, the application and energy requirements must be
considered when selecting a bistable mechanism design. One method
of increasing stability is to increase the number of legs in the
bistable mechanism. Increasing the number of legs also increases
the input force required to toggle the mechanism.
Referring to FIG. 8, another embodiment of a mechanism 410
according to the invention is depicted; the mechanism 410 may also
be sized for MEMS applications, and may also be bistable. As
depicted in FIG. 8, the mechanism 410 may receive an input force
411, and may have a shuttle 420 disposable between two stable
positions. The shuttle 420 may be connected to a first base member
422, a second base member 424, a third base member 426, a fourth
base member 428, a fifth base member 430, and a sixth base member
432.
The shuttle 420 may be coupled to the first and third base members
422, 426 by a first leg 30 and to the second and fourth base
members 424, 428 by a second leg 32. Additionally, the shuttle 420
may be coupled to the third and fifth base members 426, 430 by a
third leg 434 and to the fourth and sixth base members 428, 432 by
a fourth leg 436. The first and second legs 30, 32 may be
integrally formed with and coupled to first and second shuttle
flexural pivots 40, 42, and to first and second base flexural
pivots 44, 46. Similarly, the third and fourth legs 434, 436 may be
integrally formed with and coupled to third and fourth shuttle
flexural pivots 450, 452, and to third and fourth base flexural
pivots 454, 456.
The first, third, and fifth base members 422, 426, 430 may be
connected in series, and the second, fourth, and sixth base members
424, 428, 432 may be similarly connected in series. Thus, a first
deformable member 460, a second deformable member 462, a third
deformable member 464, and a fourth deformable member 466 are
formed; each of the deformable members 460, 462, 464, 466 is
coupled to one of the base flexural pivots 44, 46, 454, 456,
respectively. The deformable members 460, 462, 464, 466 may be like
those 60, 62 of FIG. 1, with the addition of stubs 468 to which the
base flexural pivots 44, 46, 454, 456 are attached. The stubs 468
may help to avoid plastic deformation in the junctures between the
deformable members 460, 462, 464, 466, and the base flexural pivots
44, 46, 454, 456. Without the stubs 468, stresses may concentrate
in the junctures between the deformable members 460, 462, 464, 466
and the base flexural pivots 44, 46, 454, 456.
The use of multiple sets of legs 30, 32, 434, 436 may prevent the
shuttle 420 from rotating or twisting in a non-linear path. Such
rotating or twisting may cause the shuttle 420 to toggle in an
unpredictable manner. Also, the additional legs 434, 436 increase
the amount of force required to actuate the mechanism 420. As
discussed above, the actuation force generally corresponds to the
amount of force that is required to deflect the deformable mounts
460, 462, 464, 466 enough to allow the shuttle 420, legs 30, 32,
434, 436, and flexural pivots 40, 42, 44, 46, 450, 452, 454, 456 to
linearly align at the toggle point.
The addition of two more deformable members 464, 466 constitutes
additional potential energy that must be added to the mechanism 410
by the actuating force to toggle the shuttle 420. Thus, by adding
third and fourth legs 434, 436 and third and fourth deformable
mounts 464, 466, the amount of force required to move the mechanism
410 from the first stable configuration to the second stable
configuration is roughly double that of the mechanism 10 of FIG. 1.
As a result of the greater required actuating force, greater
stability is similarly obtained. The mechanism 410 effectively has
two compliant bridges, one of which extends from the first
deformable mount 460 to the second deformable mount 462, and
another of which extends from the third deformable mount 464 to the
fourth deformable mount 466.
As shown in FIG. 8, the base members 422, 424, 426, 428, 430, 432
may take the form of enclosed anchors 422, 424, 426, 428, 430, 432.
The anchors 422, 424, 426, 428, 430, 432 may be affixed to a
silicon substrate in stationary fashion. FIG. 8 also depicts the
third and fourth anchors 426, 428 as common elements of the first
and third deformable mounts 460, 464 and the second and fourth
deformable mounts 462, 466, respectively. This allows for material
and size reduction, and also creates separately deflecting
deformable mounts 460, 462, 464, 466 for each of the legs 30, 32,
434, 436. Attaching each of the legs 30, 32, 434, 436 to a single
deformable mount 460, 462, 464, 466 simplifies the design of the
mechanism 410 and the calculation of the input force 411 required
to toggle the mechanism 410.
However, the mechanism 410 may also be designed without the third
and fourth base members 426, 428, so that the first and third legs
30, 434 are attached to a common deformable mount extending between
the first and fifth base members 422, 430, and the second and
fourth legs 32, 436 are also attached to a common deformable mount
(not shown) extending between the second and sixth base members
424, 432. The deformable mounts would operate in a manner similar
to that described above, but with a slightly different type of
deformation. Such an elongated deformable mount may beneficially
allow for further material and size reduction. Another alternative
embodiment may have a single central anchor (not shown) with two
cantilevered beams extending from opposite sides of the central
anchor. The legs 30, 32, 434, 436 may then be coupled to the ends
of the cantilever beams to provide the required inward force to
produce bistable operation.
Another way of controlling the stability of a bistable mechanism
such as the mechanism 410 of FIG. 8 is by adjusting the
orientations of the mechanism elements with respect to each other.
The relative angles of the elements control the function of the
mechanism. Various angles of the mechanism 410 may be varied
through a wide range of values to create an infinite number of
operational variations. This allows a mechanism like the mechanism
410 to be custom designed to suit individual applications and
constraints.
More specifically, the mechanism 410 may be manufactured with
certain angles 470, 472, 474, 480, 482, 484 in an undeformed
configuration, which will be assumed to be the first stable
configuration of the mechanism 410. A first base pivot angle 470
may be the angle at which the first and second base flexural pivots
44, 46 extend from the first and second deformable mounts 460, 462.
A first leg angle 472 may be the angle at which the first and
second legs 30, 32 extend from the first and second base flexural
pivots 44, 46. A first shuttle pivot angle 474 may be the angle at
which the first and second shuttle flexural pivots 40, 42 extend
from the first and second legs 30, 32. A second base pivot angle
480, a second leg angle 482, and a second shuttle pivot angle 484
may be analogous to the first angles 470, 472, 474, but with
reference to the third and fourth base flexural pivots 454, 456,
the third and fourth legs 434, 436, and the third and fourth
shuttle flexural pivots 450, 452.
If the angles 470, 472, 474, 480, 482, 484 are not selected
correctly, the mechanism 410 may not be bistable. For example, the
angles 470, 472, 474, 480, 482, 484 should all be positive, i.e.,
in the direction shown, so that the legs 30, 32, 434, 436 do not
compress into a zigzag configuration with the flexural pivots 40,
42, 44, 46, 450, 452, 454, 456 when the input force 411 is applied.
Similarly, the angles 470, 474, 480, 484 should preferably not be
too extreme to avoid zigzagging and/or the buildup of concentrated
bending stresses at the locations where the flexural pivots 40, 42,
44, 46, 450, 452, 454, 456 attach to the shuttle 420, the legs 30,
32, 434, 436, and/or the deformable mounts 460, 462, 464, 466.
The first angles 470, 472, 474 need not be the same as the second
angles 480, 482, 484. If desired, different angles may be used for
analogous parts of the mechanism 410 to obtain a specific input
force-to-displacement curve, additional stable configurations, or
the like.
FIG. 8 further demonstrates the use of the mechanism 410 as a
compliant, bistable electrical switch. In this embodiment, the
shuttle 420 may be positioned to close an electric circuit when
actuated to the second stable configuration. More specifically, the
shuttle 420 may positioned to abut an output force receiver 490, in
the form of an electrical connection 490, in the second stable
configuration. The electrical connection 490 may take the form of a
first contact 492 and a second contact 494 separated from the first
contact 492 by an air gap or an evacuated space. The shuttle 420
may be made of, coated with, or simply attached to an electrically
conductive material capable of closing and completing the circuit.
When the mechanism 410 is actuated, the shuttle 420 simultaneously
engages the ends of the first and second electrical contacts 492,
494 to close the circuit. The circuit may then be opened again by
actuating the mechanism 410 back to the first stable
configuration.
Although FIGS. 1, 7, and 8 have shown embodiments in which
comparatively rigid legs are connected by small length flexural
pivots, other configurations may accomplish bistable operation
without requiring rigid legs. For example, a single arched beam may
perform the functions of the legs as well as the flexural pivots.
Such a configuration will be shown and described in connection with
FIG. 9.
Referring to FIG. 9, another embodiment of a mechanism 510
according to the invention is depicted. The mechanism 510 may be
bistable, and may be sized for MEMS applications. Furthermore, the
mechanism 510, as shown, may be utilized as an accelerometer. The
mechanism 510 may be designed to receive an input force 511, which
may come from acceleration. The mechanism 510 may have a shuttle
520 configured to move in the longitudinal direction 12; the
shuttle 520 may have a weight 521 affixed to or integrally formed
with the shuttle 520.
The mechanism 510 may also have base members 422, 424, 426, 428,
430, 432 and deformable mounts 260, 262, 264, 266 like those of
FIG. 8. However, in place of the legs and flexural pivots of FIG.
8, the mechanism 510 of FIG. 9 may have a first arched beam 530
with a first end 532 attached to the first deformable mount 260 and
a second end 533 attached to the second deformable mount 262, and a
second arched beam 534 with a first end 536 attached to the third
deformable mount 264 and a second end 537 attached to the fourth
deformable mount 266. The arched beams 530, 534 may each have a
substantially uniform cross section.
The configuration depicted in FIG. 9 may be the first stable
configuration, and may also be the manufacturing configuration in
which no significant deformation is present. The arched beams 530,
534 may be advantageous in that their structure is very simple, and
no sharp discontinuities are present to cause stress
concentrations. Furthermore, they are comparatively easy to
manufacture. However, the arched beams 530, 534 may make the
mechanism 510 somewhat more difficult to model due to their length
and the irregularity of their deformation.
As the input force 511 is applied, the arched beams 530, 534 may be
compressed into an "S" shape. When the shuttle 520 has passed the
toggle point, the arched beams 530, 534 may move into a second
stable configuration, in which the "S" shape is maintained by the
inward pressure of the deformable mounts 260, 262, 264, 266. In the
embodiment of FIG. 9, the input force 511 may be applied by
acceleration. More specifically, as the base members 422, 424, 426,
428, 430, 432 move in a direction opposite to that of the input
force 511, inertia will act on the weight 521 to draw the shuttle
520 in the direction of the input force 511, with respect to the
base members 422, 424, 426, 428, 430, 432.
The mass of the weight 521 may be carefully selected so that the
mechanism 510 snaps into the second stable configuration when the
acceleration on the mechanism 510 reaches a certain threshold. For
example, the mechanism 510 may be used to signal a vehicle impact
for subsequent diagnosis, or to trigger safety features such as
airbags in real time. The mechanism 510 may simply be combined with
the electrical connection 490 of FIG. 8 to close a circuit upon
detection of impact. Such a bistable accelerometer may be useful in
many other applications as well. The mechanism 510 may even be
reconfigured to provide more than two stable configurations, so
that different configurations can be obtained from different
accelerations.
Like the mechanisms 10, 410 of FIGS. 1 and 8, the mechanism 510 may
also be described in terms of compliant bridges. More specifically,
each of the arched beams 530, 534 operates in conjunction with the
shuttle 520 to form a compliant bridge.
A bistable mechanism according to the invention may be triggered in
a wide variety of ways besides acceleration. With reference to MEMS
applications, a bistable mechanism may be triggered by mechanical
linear or rotary devices, electrostatic actuators such as comb
drives, or actuators driven by thermal expansion. Such actuation
will be shown and described in greater detail in connection with
FIG. 10.
Referring to FIG. 10, yet another alternative embodiment of a
mechanism 610 with bistable MEMS application is shown. The
mechanism 610 may be configured somewhat similar to the mechanism
410 of FIG. 8, with a shuttle 420 connected to first, second,
third, and fourth legs 30, 32, 434, 436 by first, second, third,
and fourth shuttle flexural pivots 40, 42, 450, 452, respectively.
However, only two base members 622, 624 are present, and the
deformable mounts 460, 462, 464, 466 of FIG. 8 have been replaced
by first, second, third, and fourth deformable mounts 660, 662,
664, 666, which are provided as examples of alternative types of
deformable mounts.
A "deformable mount" is not limited to the deformable mounts 60 62,
460, 462, 464, 466 depicted in FIGS. 1, 7, 8, and 9. Rather, any
structure that is capable as being modeled or functioning as a
spring can be used to create multiple low potential energy
positions. While the embodiments of the previous figures utilize a
fixed-fixed beam in each deformable mount, other types of
deformable mounts may be implemented.
For example, the deformable mount may be a beam that cantilevers
from a rigid surface at one end and is fixed to a small-length
flexural pivot at the other end. The bending of the beam at the
non-fixed end will provide the biasing force that creates the two
low potential energy positions. Alternatively, the deformable mount
may be a fixed-fixed arched beam or a beam that is initially
deflected. In yet another variation of the bistable mechanism, the
deformable mount may be a structure similar to the bistable
mechanism itself, but with only one stable position; the deformable
mount may simply resist any deflection from the one stable
configuration to provide biasing force. One of ordinary skill in
the art will recognize that there are many methods of creating a
force to urge a compliant bridge into multiple low potential energy
positions.
In the mechanism 610 of FIG. 10, the first deformable mount 660 has
a first compressible member 670 that extends from the first base
member 622 in cantilevered fashion to attach to the first leg 30.
Similarly, the second deformable mount 662 has a second
compressible member 672 that extends from the second base member
624 in cantilevered fashion to attach to the second leg 32. Each of
the compressible members 670, 672 may take the form of a relatively
thin beam with a looped portion; the looped portion may be
compressed to provide the biasing force to store potential energy,
thereby performing essentially the same function as the mounting
beams 58, 59 of FIG. 1.
Similarly, the third and fourth deformable mounts 664, 666 may have
third and fourth compressible members 674, 676, respectively. The
third and fourth compressible members 674, 676 may extend from the
first and second base members 622, 624 to attach to the third and
fourth legs 434, 436, respectively. Each of the compressible
members 674, 676 may take the form of a relatively thin beam with a
bend or kink to ensure that the beam will buckle under compression.
The compressible members 674, 676 may have such a shape that the
buckling is elastic over the feasible range of travel of the
shuttle 420.
The mechanism 610 may receive an input force from an actuator 680
disposed in close proximity to the mechanism 610. As mentioned
previously, a wide variety of actuator types may be used, including
micromechanical devices such as worm gears, rack and pinion
assemblies and the like, electrostatic actuators such as comb
drives, and thermal actuators. The exemplary actuator 680 of FIG.
10 is a thermal microactuator. The actuator 680 may have a shuttle
682 positioned close to the shuttle 420 of the mechanism 410 when
the mechanism 410 is in the first stable configuration. The shuttle
682 of the actuator 680 may be coupled to a first base member 684
and a second base member 686 by a plurality of expansion members
690, each of which is comparatively long and thin.
When electric current passes from the first base member 684 to the
second base member 686, the current travels through the expansion
members 690. The expansion members 690 heat up in response to the
current, and expand to press inward against the shuttle 682. The
shuttle 682 is thereby driven to move toward the shuttle 420 of the
mechanism 610. The shuttle 682 may contact the shuttle 420, and
exert pressure on the shuttle 420 until the mechanism 610 has
passed the toggle point.
After the mechanism 610 passes the toggle point, the potential
energy stored by the mechanism 610, and more specifically, stored
by the compressible members 670, 672, 674, 676, may act to move the
mechanism 610 into the second stable configuration, thereby pulling
the shuttle 420 out of contact with the shuttle 682. If desired,
the shuttle 420 may be moved back to the first stable configuration
through the use of a second actuator (not shown), or through the
application of electrical or thermal energy directly to the
mechanism 610.
In the alternative, the shuttle 682, and indeed, the entire
actuator 680, may be integrally formed with the shuttle 420 of the
mechanism 410. Thus, the actuator 680 may be used to push the
mechanism 610 into the second stable configuration, and to pull the
mechanism 610 back into the first stable configuration. Once the
current is disconnected, the expansion members 690 will cool,
thereby retracting the shuttle 682 to pull the shuttle 420 back
into its original position.
According to another embodiment, a bistable mechanism may
incorporate the functionality of an actuator. For example, such a
mechanism may have members that thermally expand under the
application of electric current to push a shuttle into a second
stable position. The shuttle may return to the first stable
position after the current is disconnected. In the alternative, the
shuttle may remain at the second stable position after the current
is disconnected, but application of current elsewhere on the
bistable mechanism may serve to return the shuttle to the first
stable position.
FIG. 11 is an alternative embodiment of a bistable mechanism 710
that employs pin joints in MEMS application. The bistable mechanism
710 is similar to the previously discussed mechanism, in that it
has a base member 712 and a shuttle 716 that are coupled together
by a flexible leg 720. However, in the present embodiment the base
member 712 and the base end 724 of the leg 720 as well as the
shuttle end 728 of the leg 720 and the shuttle 716 are coupled
together by pin joints 730, 732. The bistable mechanism 710 has a
first stable configuration and a second stable configuration that
are obtained by applying an actuation force 740 to the shuttle
716.
In the embodiment depicted in FIG. 11, the bistable mechanism 710
actuates when a determined actuation force 740 is placed upon the
shuttle 716 in a longitudinal direction 12. Similar to other
embodiments previously discussed, the bistable nature of the
mechanism, 710 is in part produced by a fixed lateral 14 distance
between the base member 712 and the shuttle 716. In a MEMS
application, the base member 712 is typically fixed to the
microchip substrate 742 or is an integral part of the substrate
742. Alternatively, the base member 712 may be fixed to another
micromechanism which may or may not be fixed to the substrate 742.
Generally, the base member 712 needs only to substantially maintain
the lateral 14 distance between itself 712 and the shuttle 716. In
FIG. 11, the shuttle 716 has a fixed lateral 14 distance from the
base member 712. This fixed lateral 14 distance is produced by the
shuttle being configured to slide on a surface 748 that maintains a
longitudinal 12 travel. Thus, the lateral 14 distance between the
base end 724 and the shuttle end 728 of the leg 720 is fixed.
This fixed lateral 14 distance allows the micromechanism 710 to
function in a bistable manner. The bistability is obtained by the
linear length of the leg 720 being longer than the lateral 14
distance between the base member 712 and the shuttle 716. The
linear length of the leg 720 is measured as the distance from the
fixed pin joint 730 to the floating pin joint, 730 add to the
length from the center of the floating pin joint 732 to the
shuttle's 732 contact with the sliding wall 748. In the
configuration depicted in FIG. 11, the linear length of the leg 720
is equal to the lateral distance between the base member 712 and
the shuttle 716 divided by the cosine of the offset angle 752
between the two pin joints 730, 732. Thus when an offset angle 752
between the pin joints 730, 732 exists, the linear length of the
leg 720 will be longer than the lateral 14 distance between the
base member 712 and the shuttle 716. This requires the linear
length of the leg 720 to compress as the shuttle 716 is biased from
the stable configuration depicted in FIG. 11 to the other stable
configuration.
As the linear length of the leg 720 compresses, potential energy
builds up within the leg 720. The potential energy is stored within
the deformed and flexed material of the leg 720. In the embodiment
of FIG. 11, the energy is stored within the curvature of the arched
leg 720. The leg 720 is depicted in FIG. 11 in the first stable
configuration that is at a relative zero potential energy position.
The potential energy is zero because the curvature of the leg 720
is at its rest state. If the leg is bent or deflected, the
potential energy will increase in the leg, causing the leg 720 to
bias back to its rest configuration. The configuration of the
micromechanism 710 depicted has two rest configurations, the first
stable configuration and the second stable configuration.
The first and second stable configurations correspond to two low
potential energy positions along the travel of the shuttle 716. The
mechanism also has a toggle point that corresponds to a high
potential energy position and is positioned between the two low
potential energy positions. Therefore, either direction the
micromechanism is biased from the toggle point will cause the leg
720 to snap to one of the two low potential energy or rest
positions. Because an object will tend to stay at the lowest
potential energy configuration until acted upon by a force, the
mechanism 710 remains stable in both configurations. While the
embodiment depicted in FIG. 11 shows an arched leg 720, any shape
of leg that is capable of compressively or deflectively storing
energy may be applied to the current bistable mechanism. For
example, a leg that is straight at the stable or rest
configurations may be employed. The leg would plastically defect or
buckle as the leg approaches the toggle point. The energy created
by the deflecting or buckling would force the micromechanism into
one of the stable configurations.
In another embodiment, the legs may be generally "V" shaped where
two straight legs intersect at an angle. Potential energy is stored
in the legs as the angle between the two legs increases or
decreases. This embodiment, however, does produce high stress
levels at the intersection point. This may cause problems at the
micro level. In yet another embodiment, different raised and
lowered contours may be applied to the sliding surface to create
high potential energy positions. This may be accomplished by
causing the leg 720 to compress as it slides over a raised contour
in the sliding surface 748. The leg 720 will tend toward a low
potential energy position on either side of the high potential
energy raised contour of the sliding surface 748.
To facilitate actuation between stable configurations and to
maintain the curvature of the leg 710, the leg 710 is coupled to
the base member 712 and the shuttle 716 through the use of pin
joints. The micromechanism in FIG. 11 implements two different
types of pin joints; a fixed pin joint 730 and a floating pin joint
732. Pin joints 730, 732 differ in design and manufacture from
macro sized pin joints. Because of the material properties of MEMS,
special designs of pin joints must be implemented.
The fixed pin joint 730 of the micromechanism 710 is made in the
layering process used in MEMS, where different layer form different
members of the joint. The fixed pin joint 730 has a central pin
that is situated within a hole of a round or otherwise shaped
socket 752. The top of the pin has an enlarged head 756 to prevent
the socket 752 from slipping off of the pin. Typically, the socket
752 is manufactured on a layer above the substrate 742 of the chip
to prevent stiction. Stiction is caused by Van Der Waals and
electrostatic forces between the members and the substrate 742.
Once stiction occurs, it is difficult or impossible to free the
MEMS member. To prevent this, the mechanism members may be
maintained above the substrate 742 and other members through the
use of dimples. A dimple is a small section of a mechanism that
extends from the bottom of the mechanism to engage the substrate
742. These dimples provide a relatively small surface area contact
with the substrate 742, such that the Van Der Waals and
electrostatic forces may be overcome to allow movement.
The floating pin joint 732 functions in a slightly different manner
than does the fixed pin join 730. The floating pin joint 732 must
not only be able to hinge two members of a mechanism 710, but it
must also be capable of sliding over the substrate 742 without
stiction problems. In one embodiment, the floating pin joint 732 is
comprised of a ring 760 rigidly attached to a pin mount 764. The
ring 760 is also rigidly attached to the shuttle 716. The pin mount
764 extends into the center of the ring 760 and a pin extends from
the surface of the pin mount 764 and toward the substrate 742. The
pin mates with a floating socket 768 that is also situated within
the center of the ring 760. The floating socket 768 has a bridging
member 772 that rigidly attaches the leg 720 to the floating socket
768. The bridging member 772 may also be configured to ride along
the top of the ring 760 as the pin, pin mount 764, and ring 760
rotate relative to the floating socket 768, bridging member 772,
and the leg 720. In one embodiment the ring 760, the floating
socket 768, and the leg 720 are manufactured from a first layer and
the pin mount 764 and the bridging member 772 are manufactured from
a second layer.
Another embodiment of a floating pin joint 732 is comprised of an
inner disk and an outer ring. The inner disk is situated within the
center of the outer ring. The inner ring is attached to a first arm
that bridges over the outer ring and the outer ring is fixed to a
second arm that extends in the opposite direction of the first arm.
The first arm further comprises a lip that cantilevers over the
inner disk to maintain their relative engagement. The outer ring
and the inner disk rotate relative to each other where the first
and second arms maintain engagement and prevent slipping.
Pin joints provide advantages in certain applications over fully
compliant joints. For example, pin joints allow for larger travel
with smaller mechanism members, when compared to fully compliant
mechanisms. Additionally, pin joints have the advantage of
providing large ranges of rotational motion with minimal effect on
surrounding components. In the present embodiment of the bistable
mechanism, the use of pin joints allows the shape and curvature of
the leg to be relatively unaffected in the first and second stable
configurations. On the other hand, a compliant joint may require a
significant section of the leg to bend and deflect to allow for the
full range of motion needed. While the bending and deflecting of a
leg in certain bistable application is acceptable, the present
embodiment relies on the shape and curvature of the leg to control
the potential energy storage. It is the control of this potential
energy that allows the mechanism to function.
Potential energy storage is controlled by changing the curvature of
the leg as it moves through the toggle point. The potential energy
stored in the leg 720 increases as the leg approaches the toggle
point and then correspondingly decreases as the leg 720 moves away
from the toggle point. The potential energy is stored by changing
the curvature of the leg away from its rest position. However if in
order to facilitate motion, the curvature of the leg continues to
deflect after the toggle point, potential energy may increase in
the leg 720 after the toggle point If the potential energy
continues to increase after the toggle point, then the mechanism
may only have one low energy position and thus no longer be
bistable. Thus for the present embodiment, it is advantageous to
maintain the curvature of the leg through the entire range of
motion. This curvature is most easily maintained through the use of
pin joints.
FIG. 12 demonstrates an alternative configuration of a bistable
mechanism 810 that uses two sets of legs that are coupled to pin
joints. The mechanism 810 is depicted in the first stable
configuration and functions similarly to the single leg embodiment
depicted in FIG. 11. This embodiment comprises a first set of legs
812 and a second set of legs 816. Each leg in the sets 812, 816 has
a base end 820 and a shuttle end 824, wherein the base ends 820 is
coupled to a fixed pin joint 826 and the shuttle end 824 is coupled
to a floating pin joint 827. Each base end 820 is connected to the
fixed pin joint 826 by a socket 828 that is attached to the base
end 820 of the legs 812, 816. The socket 828 has a hole through
which a pin protrudes (not visible in FIG. 12) to rotatably mount
the leg 812, 816 to the substrate 832. The socket 828 is capable of
rotating about the pin.
In the embodiment depicted in FIG. 12 the base member to which the
fixed pin joints 826 are attached may be a microchip substrate 832.
However, the base member can take various embodiments such as a
raised structure above the substrate 832 or a member of another
mechanism. The base member need only maintain the relative lateral
14 distance between the base end 820 and the shuttle end 824. Other
embodiments of the fixed pin joints are possible and are within the
scope of this application. Additionally, the fixed pint joint may
be replaced with a fully compliant mechanism, such as a small
length flexural pivot. While this type of joint may not be a
preferred embodiment for the given bistable mechanism 810, one of
ordinary skill in the art will recognize compliant joint designs
that will not interfere with the bistable nature of the mechanism
810.
While the base ends 820 of the legs 812, 816 are couple to fixed
pin joints 826, the shuttle ends 824 are couple to floating pin
joints 827. The floating pin joints 827 provide a rotational
coupling between the legs 812, 816 while also having the ability to
translate with the displacement of the shuttle 836. The shuttle end
824 is coupled to the bridging member 838 that is attached to the
floating socket 840. The shuttle 836 end is conversely attached to
the ring 842 and the pin mount 844. The pin extends from the
surface of the pin mount 844 into a hole in the floating socket
840. This pin engagement allows the legs 812, 816 to rotate
relative to the shuttle 836. The floating pin joint 827 may also
translate along the surface of the substrate 832 because no element
of the floating pin joint 827 is fixed to the substrate 832.
Additionally, the minimal surface engagement of the floating socket
840 and the ring 842 helps to limit stiction between the floating
pin joint 827 and the substrate 832. Thus, as the mechanism 810
toggles from the first stable configuration to the second stable
configuration, the floating pin joints 827 can translate along the
surface of the substrate 832.
FIG. 13 depicts the micromechanism 810 of FIG. 12 in the second
stable or actuated configuration. As discussed above, this figure
demonstrates that the position of the floating pin joints 827 moves
with the shuttle 836 when the mechanism 810 actuates. This can be
best viewed by comparing the longitudinal 12 position of the
floating pin joint 827 to the longitudinal position of fixed pin
joint 826. This comparison between the mechanism's 810 position in
FIG. 12 and the position in FIG. 13 demonstrates that the floating
pin joint 827 travels along the substrate with shuttle 836.
While FIGS. 12 and 13 depict the floating pin joints 827 as an
external member of the shuttle 836, the floating pin joints 827 may
be an internal structure on the body of the shuttle 836. For
example, a type of fixed pin joint that sits on top of the shuttle
836 may be implemented. However, current MEMS manufacturing
processes requires the connecting members to be manufactured of the
same silicon or other material. Therefore in order to place a type
of fixed pin joint on the shuttle 836, the fixed pin joint 826 that
is attached to the substrate 832 should be raised to the same layer
as the pin joint on top of the shuttle. In yet another embodiment,
the pin joint attached to the shuttle end 824 of a leg from the
first leg set 812 can be the same pin joint that connects a leg
from the second leg set 816. Thus, the attachment location of the
two pin joints would be the same position on the shuttle. In this
embodiment there is only one set of pin joints down the center of
the shuttle 836. The pin joint is coupled to two different legs
that move relative to each other. In a variation of this
embodiment, the two legs may share a common floating pin joint
where no shuttle is present and the floating pin joint may be the
actuation member. In yet another embodiment, the floating pin
joints may be replaced with a fully compliant joint, such as a
small length flexural pivot.
FIG. 13 further demonstrates that the curvature of the arched legs
812, 816 in the second stable configuration is substantially
similar to the curvature of the arched legs 812, 816 in first
stable configuration. As discussed above, the curvature of the
arched legs 812, 816 correspond to the linear distance between the
fixed pin joint 826 and the floating pin joint 827. Because the
legs 812, 816 have only one fixed end (the base end 820), the
rotation about the fixed pin joint 826 is in an arched or circular
path. This arched path allows for two locations of the shuttle end
824 to exist that have the same linear distance between the fixed
pin joint 826 and the floating pin joint 827. These two locations
allow the arched legs 812, 816 to be in their non-deflected or rest
states which correspond to a common curvature.
A close comparison of FIGS. 12 and 13 will reveal that there is a
slight variance in the leg curvatures between the first and second
configurations in the two drawings. This may be attributed to the
terminals 848 that the shuttle 836 abuts. To ensure proper contact
between the shuttle 836 and the terminals 848, it is preferred that
the shuttle 836 continue to bias against the terminals 848 when
substantially at the second stable configuration. In other words,
the shuttle 836 abuts the terminals 848 before the shuttle 836
reaches the second low potential energy position. As a result, in
this embodiment, the two curvatures may vary slightly.
The terminals 848, depicted in FIG. 13, are one embodiment of many
possible applications for a bistable micromechanism. The present
embodiment functions as an electrical switch. The micromechanism
810 in FIG. 12 demonstrates an open circuit configuration and the
micromechanism in FIG. 13 demonstrates a closed circuit
configuration. The shuttle 836 has a contact 852 that, when
actuated, closes the circuits as shown in FIG. 13. The terminals
848 have guiding protrusions that facilitates a proper engagement
and alignment with the corresponding contact 852.
The bistable mechanism may also incorporate other structures to
help ensure proper engagement. For example, FIG. 13 depicts a slot
860 running in the longitudinal 12 length of the shuttle 836.
Within the slot 860 is at least one guiding mount 864 that is fixed
to the substrate 832. The guiding mount 864 helps to maintain a
linear path of travel for the shuttle 836. Furthermore, the
mechanism 810 can be assisted in traveling in a linear path by
maintaining the first set of legs 812 substantially symmetric about
the shuttle 836 to the second set of legs 816. This symmetry helps
to keep the mechanism balanced during actuation. In the present
embodiment, the guiding mounts 864 are "T" shaped to prevent the
shuttle 836 from lifting from the substrate 832. One of ordinary
skill in the art will recognize that there are multiple methods of
maintaining a linear travel of the shuttle 836 by implementing
various structures and shapes. Additionally, the bistable mechanism
810 has a wide variety of applications that would be known to one
ordinarily skilled in the art, including the applications of the
fully compliant bistable mechanism 410 discussed above.
FIG. 14 demonstrates a bistable micromechanism 810 coupled to an
actuator system 870. The actuator system 870 depicted in FIG. 14 is
capable of toggling the shuttle 836, from the first stable
configuration to the second stable configuration and then back
again to the first stable configuration. The system 870 has a
toothed extension 874 that is attached to the shuttle 836. The
toothed extension 874 is capable of driving the shuttle 836 in both
directions along the longitudinal 12 axis. The toothed extension
874 is coupled to at least one gear 878, the gear having a center
hub 882. The gear 878 is capable of driving the toothed extension
874, which in turn actuates the shuttle 836. In the embodiment
shown in FIG. 14, the gears 878 are driven by thermal in-plane
micro actuators 886. The micro actuators 886 are capable of a
displacing an actuator shuttle 890 when a current runs through
them. By tangentially connecting the shuttles 890 to the gear hubs
882, the actuator 886 can drive the gear 878 by driving the gear
hub 882 for a half rotation and the letting the rotational momentum
drive the gear 878 slightly over the top of the gear hub 882. Then
when the actuator 886 retracts, it pulls the gear 878 back through
the other half of the rotational cycle.
Multiple other methods for toggling the mechanism 810 exist and are
within the scope of the present application. For example, a single
thermal in-plane microactuator may be coupled to the shuttle 836
for a single locking operation. Additional actuators may be added
to displace the shuttle 836 between stable configurations. Further,
actuators may be attached to the fixed pin joints 826 to induce a
rotational force on the pin joint 826 sufficient to toggle to
actuator. One of ordinary skill in the art will recognize that a
wide variety of embodiments exist for the bistable mechanism and
are within the scope of the present application.
While the compliant bistable micromechanism provides the ability to
toggle between two stable configurations, it is limited in the
amount of force that can be placed upon the mechanism without
toggling it to the previous configuration. In order provide a
mechanism that is capable of receiving a force larger than the
actuation force, a latching or locking mechanism needs to be
implemented. A latch mechanism is disclosed that is configured to
induce a locked configuration and an unlocked configuration by
actuating a slider in a single direction. A locking member actuates
a first distance in an actuation direction to induce the locked
configuration and the locking member actuates a second distance
induce the unlocked configuration. The second distance is a
displacement that is in addition to the first distance the lock
slider displaces. The latching mechanism may also have a detent
slider that allows the lock slider to travel in a direction
opposite the actuation direction.
An embodiment of the latching mechanism is depicted in FIG. 15.
Referring to FIG. 15, a latching mechanism 910 having a latched and
an unlatched position is depicted. The latching mechanism 910 has
lock slider 912 that is slidably disposed substantially within the
perimeter of a detent slider 916. The lock slider 912 is maintained
within the perimeter of the detent slider 916 by a raised member
920 that bridges over the lock slider 912. The height of the raised
member 920 is sized to engage a first stop 922 and a second stop
923 that are located on the lock slider 912.
The detent slider 916 is slidably disposed within a base member
924. The base member 924 may be a housing or a surface which
provides a structure from which the lock slider 912 and the detent
slider 916 may travel in relation thereto. In a MEMS application
the base member would be attached to the substrate to allow only
in-plane travel. In FIG. 15, the detent slider 916 is slidably
maintained on the surface by a bracket type base member 924. The
lock slider 912 is similarly coupled to the surface by a guiding
mount 926 fixed within a guiding slot 927. The guiding mount 926
has an overhanging head that extends over the lock slider 912 to
confine the travel of the lock slider 912 to the length of the slot
927.
The lock slider 912 also has a locking mount 928 that is configured
to engage a grasping member 932. In the embodiment shown in FIG.
15, the grasping member 932 is a mechanism that has a fixed end and
a free end that are separated by a generally flexible arm. The
grasping member 932 comprises an engagement member 936 and a
disengagement member 940 that are located at the free end. The arm
is also a compliant mechanism, in that it pivots about a single
piece integrally formed member. Additionally, the grasping member
932 may be a compliant member because it 932 resist deflection in a
spring-like manner without multiple parts or additional force
absorbing members.
In the embodiment of FIG. 15 the grasping member 932 pivots about a
mounting member 944 that is in a fixed location. The engagement
member 936 is configured to engage the locking mount 928 in a
locked configuration and the disengagement member 940 is configured
to engage the locking mount 928 in an unlocked configuration. The
locked configuration and the unlocked configuration can be induced
by an actuation force on the lock slider 912 in a single actuation
direction. The detent slider 916 is also configured to engage the
engagement member 936 of the grasping member 932 to maintain the
unlocked configuration. Once the detent slider 916 engages the
engagement member 936, the lock slider 912 can be retracted from
the grasping member 932 by a biasing force that may or may not be
induced by an actuator.
The relative configurations and motion of the members of the
latching mechanism 910 may be best illustrated by referring to FIG.
16. FIG. 16 is an operational view of the latching mechanism
represented by sub-FIGS. 16A E. FIG. 16A is the initial
configuration of a lock slider 910 that is symmetric about the
lateral 14 length of the lock slider 912. This symmetry provides
two grasping members 932 that are capable of engaging the locking
mount 928. In this configuration, the lock slider 912 and the
associated locking mount 928 are not engaging the grasping members
932. This is the initial unlocked configuration.
The lock slider 912 engages the grasping members 932 in FIG. 16B
upon receiving a locking force in the lateral 14 direction. The
locking force is sufficient to displace the lock slider 912 a first
distance. The locking force need only be of a magnitude capable of
sliding the lock slider a first distance and deflecting the
grasping members 932 is a locking deflection which induces a locked
configuration. However, the actuation distance of the locking force
is preferably the minimal length required to engage the locking
mount 928 to the grasping members 932. In the embodiment depicted
in FIG. 16, the first distance is preferably identified as the
distance required to engage the locking mount 928 to the grasping
members 932 or of a distance equal to the distance between the
first stop 922 and the raised member 920.
In this locked configuration, as depicted in FIG. 16B, the latching
mechanism 910 is substantially more stable that a typical bistable
mechanism. Because the locking mount 928 has an interference
engagement with the engagement members 936, the engagement is
capable of sustaining a force opposite the actuation direction that
is larger than the actuation force. This is in contrast to a
typical bistable mechanism where the force required to actuate the
mechanism back to its first stable configuration is equal to or
less than the force that originally actuated the mechanism to the
second stable configuration. Thus, the amount of force that can be
applied to the lock slider 912 in a direction opposite the
actuation direction is only limited by the structural and
engagement properties of the grasping member 932 and the locking
mount 928.
In a preferred embodiment, the engagement of the grasping members
932 and the locking mount 928 is accomplished by two members
locking in the in the same plane. If one member slips above or
below that plane, then the lock slider 912 and the grasping member
932 will disengage. The disengagement force would thus be the force
required to induce an out-of-plane 16 slipping between the two
members. However, various geometric features can be implemented to
the latching mechanism 910 to prevent slipping. For example, an
overhanging lip may be added to prevent slipping or the engagement
member 928 may have a groove that prohibits out of plane
slipping.
Alternatively, the force that the lock slider 912 is capable of
sustaining may be limited by the weakest failure mode of the
grasping member 932. In the embodiment depicted in FIG. 16, the
weakest failure mode may be the tensile strength of the thin
flexible arms 952. If a force is placed upon the lock slider 912
that induces a tensile force in the thin flexible arms greater than
the maximum tensile load, then the locking mount 928 will be
released from the grasping member 932, and will return to the
original position of FIG. 16A. Additionally, stress concentrations
in the engagement members 936 or in the intersection of the thin
flexible arms 952 with the mounting members 944 may cause the
members to fail and allow the lock slider to return to the original
position of FIG. 16A. Such stress concentrations may be caused by
the geometry of the grasping members 932 or the locking mount 928.
Further, fatigue stresses in the members may also create failure
location in the latching mechanism 910.
While, the latching mechanism 910 is capable of maintaining a large
force in a direction opposite the actuation direction, the latching
mechanism is capable disengaging the grasping member 932 by a force
generally equal to the actuation force. To disengage the lock
slider 912 from the grasping members 932, a force is place upon
lock slider 912 in the lateral 14 actuation direction that
displaces the lock slider 912 a second distance. As depicted in
FIG. 16C, the second distance is a distance capable displacing the
lock slider 912 a distance sufficient to engage the disengagement
members 940 of grasping members 932. The detent slider 916 is
configured to react to the second displacement of the lock slider
912, wherein the reaction displaces the detent 916 slider from the
position depicted in FIGS. 16A and 16B to the position depicted in
FIG. 16C.
In the embodiment shown, the detent slider 916 is displaced the
second distance when the first stop 922 abuts the raised member
920. A discussed previously, the lock slider 912 is configured to
slide within the detent slider 916. The raised member 920 is the
section of the detent slider 916 connecting the two sides of the
detent slider 916 and bridging over the lock slider 912. The raised
member 920 is situated above the lock slider 912 at a height
sufficient allow the lock slider 912 to slide relative to the
detent slider 916. However, the raised member 920 is also of a
height sufficient to abut the stops 922, 923 in response to a
determined movement of the lock slider. In FIG. 16C, the first stop
922 abuts the raised member 920 when the lock slider 912 displaces
the second distance. The second displacement distance drives the
detent slider 916 to engage the engagement members 936 of the
grasping members 932. A shown in FIG. 16C, the detent slider 916
lodges between the two grasping members 932, such that when the
lock slider 912 retracts from the disengagement members 940 the
grasping members 932 are maintained in an unlocked configuration by
the detent slider 916.
The locked and unlocked configurations, in the embodiment shown,
relate to the relative position of the grasping members 932 to the
lock slider 912. The locked configuration, FIG. 16B, occurs when
the locking mount 928 engages the engagement mounts 936 of the
grasping members 932. In order to engage the engagement mounts 936
the locking mount 928 must first spread apart the grasping members
932 that are spaced more narrowly than the width of the locking
mount 928. As the locking mount 928 first abuts the grasping member
932, the angled edged of the locking mount 928 spread apart
grasping members 932 until the flat edge of the locking mount 928
reaches the flat edge of the engaging mounts 936, as depicted in
FIG. 16B. This flexing and spreading of the grasping members 932 to
engage the locking mount 928 and the resulting engagement is
referred to herein as the locking deflection. The locking
deflection of the grasping members 932 allows the lock slider 912
and the grasping members 932 to create a locked configuration.
The unlocked configuration, FIG. 16C, occurs as the lock slider is
displaced in the actuation direction and the locking mount 928
abuts the disengagement members 940 of the grasping members 932. In
the embodiment shown, the disengagement member 940 is an angled
structure where the angle is substantially parallel to the angled
edges of the locking mount, as shown. The disengagement members 940
of the two grasping members 932 are spaced at a distance narrower
than the width of the locking mount 928. The difference in width
between the locking mount 928 and the grasping members 932 causes
the angled edges of the locking mount 928 to spread apart the
disengagement members 940 and resultantly spread apart the grasping
members 932 in an unlocking deflection. This operates in a ramping
manner, such that as the disengagement member 940 is driven further
into the angled edge or ramp, the grasping members 932 move further
away from their rest or locked configuration.
In the embodiment shown, the spacing apart of the two grasping
members 932 in the unlocking deflection is larger than the spacing
of the two grasping members 932 in the locking deflection. This
difference in spacing between the grasping members 932 in the
locking deflection and grasping members 932 in the unlocking
deflection is of sufficient spacing to allow the locking mount 928
to retract in a direction opposite the actuation direction without
re-engaging the locking mount 928. As depicted in FIG. 16D, the
grasping members 932 are maintained in the unlocking deflection by
the detent slider 916 at a spacing larger than the width of the
locking mount 928.
With the spacing of the grasping members 932 maintained by the
detent slider 916, the lock slider 912 can retract a distance such
that when the detent slider 916 disengages the engagement members
936, the locking mount will not re-engage the engagement member
936. To disengage the detent slider 916 from the grasping members
936, the lock slider is equipped with a second stop 923. The stop
923 is raised above the surface of the lock slider 912 at a height
sufficient to abut the raised member 920 of the detent slider 916.
Thus, as the lock slider 912 retracts from the grasping members
932, the second stop 923 abuts the raised member 920 and retracts
the detents slider 916 from the engagement members 936 of the
grasping members 932. Once the detent slider 916 retracts, the
grasping member returns to its initial unengaged configuration,
FIG. 16E.
One advantage of the present latching mechanism is that the
mechanism may lock and unlock by a single directional force. FIG.
16 demonstrates this single directional force by the lateral 14
force arrows depicted in sub-figure 16B and 16C. The first force
956 induces a translation of the lock slider 912 the first
distance, as shown in FIG. 16B. The force need only be of
sufficient magnitude and distance to induce an unlocking deflection
in the grasping member 932 to engage the locking mount 928 in the
locked configuration. This same force creating source that induced
the locked configuration may be used to induce the unlocked
configuration. This second force 966, in the embodiment shown, may
also act upon the lock slider 912 in the same direction as the
first force 956. The second force induces a displacement in the
lock slider 912 to translate a second distance, where the second
distances is in addition to or longer than the first distance from
the initial configuration in FIG. 16A.
The difference in displacement length of the lock slider 912
between these two forces 956, 960 is demonstrated by the relative
size of the arrows in FIGS. 16B and C. The first force 956 arrow is
shorter than the second force 960 arrow. This indicates that second
displacement is further from an initial reference point than is the
first displacement. Thus, the lock slider 912 is further from its
initial configuration, FIG. 16A, at the second displacement, FIG.
16C, than it is at the first displacement, FIG. 16B. While the net
distance of the second displacement is larger than the first
displacement, the actual distance travel by the lock slider to
induce the unlocked configuration need not be longer than the
actual distance traveled to induce the locked configuration. The
distance the lock slider 912 travels from the initial configuration
to the locked configuration may be longer or shorter than the
distance the lock slider 912 must travel from the locked
configuration to the unlocked configuration, depending upon
embodiment.
While a single force actuation is capable of inducing a locked and
unlocked configuration in the mechanism, the force in a direction
opposite the actuation direction is required to retract the lock
slider 912 which in turn retracts the detent slider 916. Various
embodiments may be applied to the present mechanism to provide this
retracting force without the necessity of additional actuators. In
one embodiment, the latching mechanism is microelectromechanical
mechanism that is located on a microchip. In this embodiment,
limiting actuators is important to size and power restrictions.
In a MEMS application, the first and second forces 956, 960 may be
induced by single directional actuator. One such actuator is the
amplified thermal in-plane microactuator 970 as depicted in FIG.
17. The actuator, as shown, comprises three non-amplified thermal
in-plane microactuators 972, 974 that are connected in an amplified
configuration. The amplified configuration is created by coupling
the base members 976 of a central actuator 974 to the shuttles 980
of two side actuators 974. When the shuttles of the side actuators
974 actuate, they amplify the displacement of a central shuttle 982
that is coupled to the lock slider 912.
The thermal in-place microactuators 972, 974 actuate their shuttles
980, 982 when a current is passes through opposing base members
976, 984. The shuttles 980, 982 will actuate a distance that
corresponds to the amount to current within the each actuator.
Thus, simultaneously applying a current through all three actuators
972, 974 will cause the central shuttle 982 of the amplified
actuator 970 to displace a first distance. If that current is
increased, then the actuation distance will correspondingly
increase.
Once the current is removed, the central shuttle 982 will return
back to its unactuated position. The actuator 970 requires no
additional force or energy to return to the initial configuration.
Potential energy is generated when the shuttle 982 is displaced.
The potential energy is then released, driving back the shuttle
with a determined force to the initial configurations. The force is
sufficient to retract any member, such as a lock slider 912, that
is coupled to the central shuttle when the current is removed.
When the amplified thermal in-plane microactuator 970 is attached
to the lock slider 912, a current of a determined magnitude within
the actuator will displace the lock slider 912 a first distance
until it engages the grasping member 932. The current source may
then be removed from the amplified actuator 970. Because the lock
slider 912 is locked to the engagement members 940 of the grasping
members 932, the microactuator cannot return to the unactuated
position. Thus, the potential energy generated by actuating the
central shuttle 982 is stored by the lock slider 912 and grasping
member 932 engagement.
A second current, that is large than the first current, may next be
applied to the microactuator to actuate the shuttle a second
distance that is further from the unactuated distance than is the
first distance. Because the central shuttle 982 is already locked
at the first distance, energy is only need to actuate the central
shuttle 982 the difference between the first distance and the
second distance. This second distance drives the lock slider 912
into the unlocked configuration which in turn drives the detent
slider 916 into an unlocked engagement with the grasping member
932. Once the current grasping members 932 are in their unlocking
deflection the current may be removed. Because the lock slider 912
is no longer engaged with the engagement members 936, the potential
energy in the amplified actuator 970 retracts the central shuttle
982 and the attached lock slider 912 to the initial position. While
retracting, the second stop 923 of the lock slider 912 abuts the
raised member 920 of the detent slider 916 to retract the detent
slider 916 from the grasping member 932.
Other methods of creating a reactive force on the latching
mechanism 910, without the necessity of additional actuation
members, are possible. For example, the lock slider 912 may be
attached to a spring member that elongates as the lock slider
travels the first and second distances. Once the actuation force is
removed, the spring will retract the lock slider 912. Further, a
spring member may be place in a configuration where the spring
compresses as the lock slider 912 travels the first and second
distances. Once the actuation force is removed, the spring member
will bias the lock slider 912 to its initial position. The spring
member may be any number of members known to one of ordinary skill
in the art. For example, a simple spring or an elastic member could
be used to create the retracting force. In MEMS applications, a
system of small length flexural pivots could be used to create a
spring type force on the lock slider 912. These spring member
applications would allow the actuation member that locks and
unlocks the mechanism to not be rigidly attached.
While it is preferably in one embodiment for only a single
directional actuator to be used in the present latching mechanism,
multiple actuators or force creating devices can be used to induce
the locked and unlocked configuration as well as retracting the
lock slider 912 and the detent slider 916. For example, in a macro
embodiment an operator's hand could be used to lock, unlock, and
retract the mechanism. In another embodiment, the reaction force of
an impulse force acting upon the lock slider 912 or other members
could retract the lock slider 912 and the detent slider 916. In yet
another embodiment, the lock slider 912 may be mounted in a manner
so that gravity retracts the lock slider 912 and the detent slider
916. In this configuration, the detent slider 916 would be
configured such that it would not disengage the grasping member 932
because of gravity, but would disengage when abutted by the lock
slider 912. This may be accomplished by lower mass of detent slider
916 when compared to the lock slider 912 or by a high coefficient
of friction material located on the engagement members 936.
FIG. 18 demonstrates and isometric view of a preferred embodiment
of the latching mechanism, wherein the mechanism has a lock slider
912, a detent slider 916, and at lest one grasping member 932.
However, a significant number of variations of this latching
mechanism can be created by modifying various elements of the
mechanism. Many of these embodiments can be captured in a
discussion of the method of latching a mechanism disclosed herein.
First, a lock slider 912 or similar member is displaced a first
distance in an actuation direction to engage a grasping member 932.
The lock slider 912 and grasping members 932 may be of any
structure or configuration that allows the two members to engage.
This engagement may be within a plane defined by the longitudinal
12 and lateral 14 datum lines or may be in an out-of-plane 16
direction, perpendicular to the plane.
Next the lock slider is displaced a second distance in the same
direction as the first displacement to create an unlocked
configuration. Similar to the locked configuration, the unlocked
configuration can occur in any manner that allows the lock slider
912 to disengage from the grasping member 932, within the
longitudinal 12 and lateral 14 datum line plane or out of this
plane 16. Then, the detent slider 916 is displaced a third distance
in the same direction as the first and second directions to
maintain the unlocked configuration of grasping member 932. This
may be accomplished in many ways beyond simply wedging the two
grasping members apart as depicted in FIG. 16C. Additionally, the
step of displacing the lock slider 912 the second distance and the
step of displacing the detent slider 916 the third distance may
occur simultaneously. Further, the second distance may equal the
third distance in some embodiments. Having these two distances
equal may be desired in applications where the distance an actuator
is allowed to travel is limited.
Finally, the lock slider 912 is displaced a fourth distance that is
in the opposite direction of the first, second, and third
directions. This displacement of a fourth distance is sufficient to
disengage the grasping member 932. Additional steps may also be
present in the disclosed process, such as, the detent slider 916
may be displaced or retracted in a direction opposite the first,
second, and third directions. When the detent slider is retracted,
it disengages the grasping member 932 in the unlocked
configuration. This process may also occur simultaneously with the
step of displacing the lock slider 912 the fourth distance. The
process described above is not intended to be limited by the
structure described above. The process need only provide for a
method of locking and unlocking a latching mechanism by applying a
force in a single direction.
Other embodiments, beyond what are depicted in the figures may be
used in the latching mechanism. Some embodiments may not include
all members as depicted in the figures. For example, the latching
mechanism may only include a lock slider 912 and a grasping member
932. This mechanism would operate in a similar manner as the
embodiment depicted in FIG. 18, except that detent slider 916 would
not be required to maintain the grasping members 932 in an unlocked
configuration. The grasping members 932 need only be maintained in
an unlocked configuration for an amount of time sufficient to allow
the lock slider 912 to retract from the grasping members 932.
To maintain the grasping members 932 in an unlocked configuration
for a duration of time, a dampening member could be attached to the
grasping members 932 to prevent them from returning to the locked
configuration when the lock slider 912 is removed. The grasping
member 932 would be induced into the unlocked configuration, as
discussed above. However, once the lock slider 912 induces the
unlocking deflection in the grasping members, in need only be
displaced in the direction opposite the actuation direction before
the dampened grasping members 932 return to the locked
configuration. This dampening may be obtained by attaching
fasteners to the grasping member 932 than dampening their motion
from the unlocking deflection to the locking deflection in the
longitudinal direction 12. Alternatively, the material of which the
grasping members 932 are comprised may have dampening properties
that causes the grasping members 932 to return slowly to the
locking deflection. In some embodiments the latching mechanism may
be made of plastics, metallic, or silicon material. In yet another
embodiment, the grasping members 932 may be submerged in a fluid
that dampens the movement of the grasping members 932. Various
structural members could be added to the latching mechanism to
assist in the process.
In other variations of the latching mechanism, the unlocking
deflection need not be induced by the lock slider 912 abutting the
disengagement members 940 of the grasping members 932. The present
mechanism encompasses any method of opening grasping members 932 or
disengaging the lock slider 912 that may be accomplished when
moving the lock slider 912 or the detent slider 916 relative the
grasping members 932. For example, the detent slider 916 may have a
deflecting member, such as a protruding arm, that engages a
disengagement member on the grasping member 932 to cause an
unlocking deflection. In another example, the disengagement members
932 may have a deflecting member that engages a disengagement
member on the lock slider 912 of the detent slider 916. This could
be in the form of a pair of rigid arms extending from the grasping
member 932 that engage a ramped section to the detent slider 916
unlock the grasping member 932.
In the embodiment depicted in FIG. 18, the grasping members 932 are
induced into the unlocking deflection by the angled edge of the
locking mount 928. However, various other method of inducing the
unlocking deflection can be accomplished by varying the structure
of the lock slider 912. Various extending structures and ramped
member can be employed to induce the unlocking deflection in
grasping members 932. One ordinarily skilled in the art will
recognize that there are many variations to the invention that may
be accomplished without departing from the latching mechanism
disclosed.
In yet another variation of the mechanism, the locking mount 928
may deflect to engage rigid grasping members 932. The locking mount
928 and the grasping members 932 need only deflect relative to each
other, such that they interlock one with the other. The locking
mount 928 could simply be a part of a flexible member that is
deflected into a locking deflection with the grasping members 932.
The locking mount 928 could have a dampening member attached that
allows the locking mount 928 to remain in the unlocked
configuration for a time sufficient to retract the lock slider 912
from the grasping member 932. Alternatively, the detent slider 916
may engage the locking mount 928 to maintain the unlocked
configuration until the lock slider 912 is retracted.
In another embodiment, the locking mount 928 need not be on the
front section of the lock slider 912. The locking mount may be a
number of notches or channels in the side of the lock slider.
Additionally, the grasping members 932 may have a notch on top of
the lock slider 912 for an out-of-plane 16 engagement with the lock
slider 912. Multiple variations of locking mount 928 or any section
of the lock slider 912 to the grasping members 932 are possible and
are within the scope of this application. In yet another variation
of the latching mechanism, the position of the lock slider 912
relative to the detent slider 916 may be reversed. The detent
slider 916 may be slidably situated within the locking mount 912.
The mechanism would simply operate similar to the embodiment of
FIG. 16.
The structure and the operation of the grasping members 932 could
be easily varied to create alternative embodiments of the present
mechanism. In the embodiment shown in FIG. 18, the grasping
mechanism 932 is a complaint mechanism where the thin flexible arm
952 provides a flexible joint. However, other non-complaint
structure could be employed as well as alternative embodiments of
the compliant grasping member 932. For example, the grasping member
932 could be a spring loaded pivoting mechanism with two engagement
members 936. Alternatively, the engagement members 936 could be
configured to face away from each other to engage to the locking
mount 928.
Besides the variations of the locking and unlocking structure of
the latching mechanism, the raised member 920 and the stops 922,
923 may also be varied. For example, the stops may be mounted on
the sides of the lock slider 912 in such manner that it engages a
member of the detent slider 916 to drive the slider in the
operation of the mechanism. In yet another variation, an actuator
coupled to the mechanism may selectively abut different members
during different displacement, thus eliminating the stops. For
example, an actuator could be configured to drive the lock slider
912 a first distance, but then actuate the lock slider 912 and the
detent slider 916 together the second distance. This could be
accomplished by adding a structure to the detent slider 916 that
abuts the actuator during the displacement of the second distance.
Alternatively, the actuator could only drive the detent slider the
second distance and a stop on the detent slider 916 could drive the
lock slider 912 the first distance. Various shaped and oriented
protrusions or structures could be employed to cause the detent
slider 916 to react to the movement of the lock slider 912.
In generating variations of the latching mechanism, varying the
orientation of the mechanism should be considered as a method of
generating a large number of embodiments. The mechanism as
described in FIG. 18 is substantially in-plane, meaning that most
of the movement occurs in a single plane. However, the engaging of
the locking mount 928 to the grasping members 932 could be
accomplished by changing the orientation of the operation of the
mechanism members. For example the mechanism could be simply
rotated by 90.degree. about the lateral axis 14. Thus, the locking
and unlocking of the mechanism could occur out-of-plane. The detent
slider 916 might simply be a lifting ramp that raises the locking
mount 928 or the grasping member 932 above the engagement plane to
allow the mechanisms to retract from each other.
The mechanisms disclosed herein may be modified in many other ways
to suit a wide variety of applications. The invention may be
embodied in other specific forms without departing from its
structures, methods, or other essential characteristics as broadly
described herein and claimed hereinafter. The described embodiments
are to be considered in all respects only as illustrative, and not
restrictive. The scope of intellectual property rights is,
therefore, indicated by the appended claims, rather than by the
foregoing description. All changes that come within the meaning and
range of equivalency of the claims are to be embraced within their
scope.
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